The AirGun Guild

General Category => PCP, C02, and Helium Powered Airguns => Topic started by: rsterne on June 14, 2017, 04:34:43 PM

Title: Any Interest in 6mm ? - Build Thread
Post by: rsterne on June 14, 2017, 04:34:43 PM
I have had a few guys ask about the idea of making a 6mm PCP, and it has aroused my curiousity, so I did some research.... I knew that LW made barrels in various twists (8, 9, 10, & 14") but I had never seen one in TJ's list, so I contacted Mike and it turns out that he has a mandrel to make them with 0.237" lands and 0.243" grooves, with a 10" twist.... They can be made in 1/2" and 9/16" OD, and he has a 9/16" in stock.... Then I started looking around for moulds to cast bullets, and I found these....

The first one is a Lyman 225107, interpolated out to a larger diameter by NOE.... It says it weighs 46 gr., but they currently have no stock in the store....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20NOE%2046%20gr_zpsbltyoemh.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20NOE%2046%20gr_zpsbltyoemh.jpg.html)

The second one is a scaled down Lyman 257420, done at the request of Jack Bowman (Scandalous Airguns).... Aresenal have this mould available to order, listed at 60 gr....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20Arsenal%2060%20gr_zpst0kla0pm.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20Arsenal%2060%20gr_zpst0kla0pm.jpg.html)

The third one is listed as a 73 gr., and is also out of stock at NOE....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/6mm%20NOE%2075%20gr_zpsrkrxr4gl.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/6mm%20NOE%2075%20gr_zpsrkrxr4gl.jpg.html)

I scaled down my .257 cal 78 gr. BBT, and have sent the drawing to Al to add to the AirGun Discussion Section on the NOE Forum.... It looks like this....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/NOE%20243%20cal%2065%20gr_zpsn1sevxzd.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/NOE%20243%20cal%2065%20gr_zpsn1sevxzd.jpg.html)

All of these should work just fine in Mike's 10" twist barrel.... According to my "lofty goal" PCP spreadsheet, with a 24" barrel at 3000 psi, and bore-sized porting, it should be possible to hit about 139 FPE.... In reality, that means you could probably do that with a 28" barrel, with the gun tuned to the max.... It should put the mid 900's within reach with my 65 gr. BBT with a 24-28" barrel at 3000 psi.... In other words, without going to ridiculous barrel lengths or pressures, any of the above bullets should be usable.... with the 46 gr. only requiring maybe 2200 psi or so....

Anyways, I thought I would throw this idea out there for everyone to chew on.... If there is enough interest, I'm sure we could get Al to put the BBT in a Group Buy, and the others into Inventory Runs.... I already started a thread at NOE to express your interest in the 46 gr. in hopes of getting an Inventory Run started....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on June 16, 2017, 04:51:02 PM
I spent the day today drawing out a general arrangement of what I might build for a 6mm this winter.... Here is what I came up with so far.... I used my typical reversed tank block to keep the weight of the bottle centered.... and I may use a 1.25" OD x 0.095 wall 2024-T3 tube to keep the weight down....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Sporter_zpsoihmeiqp.jpg.html)

I have already ordered a tank from AliExpress.... its a 500 cc Carbon Bottle rated at 300 bar.... the plan is to have an adjustable regulator built into the tank block, feeding a 150 cc plenum at about 200 bar.... I would like to use 3mm thick carbon fibre sleeve on the 14mm OD barrel, so the OD will be 20mm (over 3/4").... which should make it VERY stiff.... The plan is to use a PRod trigger group and an AR style stock in line with the main tube.... That will put the adjuster for the SSG inside the buffer tube.... A Cothran valve will handle the air delivery, with it's 0.257"ports perfect for the job.... If I can arrange it, I will get two 10" twist barrels, one in 6mm and the other in .257 cal., both 28" long.... The goal is to drive my 2.5 cal long BBTs at 950 fps, meaning about 130 FPE in 6mm and 156 FPE in .257....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Christopher on June 16, 2017, 06:51:27 PM
I like winter; hunting, no ticks, snow(gimme a break, I'm from Ky) and another air gun build from Bob. Sounds like a very interesting project. Looks like a good plan you have there.......especially the 6mm. Which bullet mold are you thinking about going with?

Chris
Title: Re: Any Interest in 6mm ?
Post by: rsterne on June 16, 2017, 07:58:28 PM
For sure the 60 gr. Bowman, because it is available.... Hopefully I can convince Al to take the BBT to a Group Buy....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Alan on June 17, 2017, 04:07:22 AM
The you can add a 7 mm, and a .270, and.......
Title: Re: Any Interest in 6mm ?
Post by: rsterne on June 17, 2017, 08:11:16 AM
I already have a 7mm....  ::) .... realistically it's more power than I need.... but it was fun to build....  8)

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on July 13, 2017, 02:17:14 PM
I ordered a couple of 1M pieces of Carbon Fibre tubing from China through eBay.... Excellent service, less than 2 weeks to receive them.... I can't believe how stiff this tubing is....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/14%20mm%20x%2020%20mm_zpshccqe0dp.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/14%20mm%20x%2020%20mm_zpshccqe0dp.jpg.html)

It is 20mm OD and 14mm ID, so that means the wall thickness is nearly 1/8".... It is about the same stiffness as steel tubing at a fraction of the weight, and will make the barrel incredibly stiff.... I was talking to Mike at TJ's, and he thinks he can hammer the barrel down to 14mm to fit inside the tubing, I am sending him the 6" long piece in the photo as a sample....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Christopher on July 13, 2017, 07:20:56 PM
You plan on epoxying that cf sleeve to the barrel or use it to tension the barrel with it?

Chris
Title: Re: Any Interest in 6mm ?
Post by: rsterne on July 13, 2017, 08:09:28 PM
It will be glued to the barrel with Loctite 638 (Green)....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on August 15, 2017, 01:49:31 PM
I got my barrels today from TJs.... Mike did a fantastic job of hammer-forging them to fit the sample piece of 14 mm ID Carbon Fibre Tubing I sent him.... Both the 6mm and .257 barrels I ordered are a perfect slide fit inside the CF sleeve.... They are both a 10" twist, and the blanks are 29" long....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/14mm%20OD%20Barrels_zpsgulggcha.jpg.html)

I am slowly collecting the parts I need for this winter's projects, this was a big step along that path....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Dairyboy on August 15, 2017, 02:03:50 PM
Very nice!
Title: Re: Any Interest in 6mm ?
Post by: rsterne on August 23, 2017, 03:10:26 PM
Here is the stock I ordered from DHGate, along with the buffer tube (Mil-Spec).... The fit is perfect, with about 3" adjustment in the LoP, and almost an inch of vertical adjustment for the comb height....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Stock_zpsfpojoucv.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Stock_zpsfpojoucv.jpg.html)

The stock / buffer tube assembly weighs just 1 lb. 5 oz.... and should look great with the PRod trigger group I plan on using on this build....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Christopher on August 23, 2017, 06:22:38 PM
Looking great Bob.....don't know how I did it but missed your post about the barrels. Looks like the chips are gathering for ya. You gonna keep the barrels the full 29"?

Chris
Title: Re: Any Interest in 6mm ?
Post by: rsterne on August 23, 2017, 09:40:32 PM
Aiming for 28"..... not sure yet

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on September 18, 2017, 01:49:00 PM
The mould for the 74 gr. FN, available as GC or PB, and also with a Lyman HP Pin, are now in the store at NOE.... along with the shortened version I requested....

http://noebulletmolds.com/NV/index.php?cPath=25

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on November 30, 2017, 02:57:42 PM
I got all my material for this build a couple of days ago, and decided the first thing to do was to turn down the back of one of the tubes to fit the stock.... I got a piece of 1.25" OD x 0.120" wall 2024-T3 tubing from Lloyd Sikes, which I plan to use for the .257 version, as I am going to build two guns at the same time.... The 6mm will be a regulated gun, using the 500 cc 4500 psi CF tank I got earlier.... and the .257 version will be an unregulated version having a 300 ccc reservoir that can be filled to 4500 psi.... I hope to tether it at about 3800 psi.... The straight tube, unregulated .257 version will look something like this....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Tethered%202_zps6rnaalbw.jpg.html)

The tube is long enough, and a thick enough wall, that I was able to turn down the back 7" to 1.15" OD to fit inside an AR style stock.... It will be used directly over the tube, no separate buffer tube or threaded attachment required.... I used a steady rest on the lathe to support it (since it won't fit through my headstock) and turned down the butt end.... Here is a photo of the stock slid into place.... There is still 0.070" of wall remaining, so plenty of strength.... Note you can't do this with a 1.25" OD x 0.095" wall tube, because the remaining wall would be too thin.... so the 6mm version which uses that tube will have to have a conventional threaded adapter to hold the buffer tube assembly....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tube%20Turned%20Down_zpshpc4yf21.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tube%20Turned%20Down_zpshpc4yf21.jpg.html)

With the tube slid in until the back of it hits inside the back of the stock, there is a bit under 1/4" of smaller OD tube showing, and the trigger will be mounted so that the LoP can be adjusted from 12 to 16".... At a 14" LoP it will look about like in the photo.... I have to mount a piece of aluminum barstock on the bottom of the tube to prevent rotation of the stock, and provide holes for the fore-and-aft adjustment feature.... The stock can be slid right off the back for access to the preload and gap adjustment of the SSG using a socket and/or screwdriver.... I will be using Prod trigger groups on both builds, with a taller sear supplied by Lloyd, which is intended for the 0.095" tube wall.... Since this tube is thicker, I will be milling a flat on the bottom of the tube and the top of the trigger group to get the correct sear engagement....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on December 02, 2017, 03:32:21 PM
I finished the machining to mount the stock and pistol grip today.... I decided to lengthen the locking pin by 3/16" and simply drill holes in the tube for the adjustable stock positions.... The locking pin is 5/16" diameter, so all I did to lengthen it was drill and tap it 10-32 and installed a short SHCS.... The head is 3/16" thick, exactly the length I needed.... I drilled seven 5/16" holes on 5/8" centres, so I have 3.75" of adjustment for the LoP.... In order to keep the stock from rotating I milled a short block of aluminum 1/2" wide x 3/8" tall, which I attached to the back of the tube with two low-profile 6-32 SHCSs.... The block prevents the stock from pulling right off the end while adjusting it, unless you lift up on the front of the adjusting lever, the same way the stock works on an AR buffer tube....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tube%20Machined%20for%20Stock%20and%20Grip_zpshrkmrh9q.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tube%20Machined%20for%20Stock%20and%20Grip_zpshrkmrh9q.jpg.html)

I laid out the location of the trigger group so that my LoP is adjustable from 12" (mostly for transporting it) to 15.75".... I drilled and tapped the mounting holes in the tube for the trigger group, and milled the slot for the sear.... The photo below shows what the stock and grip look like mounted to the main tube.... set for a 14.5" LoP, which is what I use most of the time....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Stock%20and%20Grip_zpsm29bqrtl.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Stock%20and%20Grip_zpsm29bqrtl.jpg.html)

I'm very happy with the appearance, simplicity, light weight and the ergonomics, and I will set up the 6 mm bottle gun with the same dimensions....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on December 03, 2017, 02:19:31 PM
The bottle gun version uses a 0.095" wall tube, which would be too thin if I turned the outside down to fit inside the AR stock.... Therefore I have to use a buffer tube to mount it, and that requires an adapter to the MRod size tube.... Here is what it looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Stock%20Adapter_zpseebcxait.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Stock%20Adapter_zpseebcxait.jpg.html)

It was made from a piece of bar stock, turned down to 1-3/8" OD for 1" of length, and that portion drilled out to 1-1/8" and then tapped 1-3/16"-16 TPI to fit the buffer tube threads.... I have a maximum of 5/8" thread engagement.... The adapter was drilled through to 19/32" and then tapped to 5/8"-28 TPI for my SSG gap adjuster.... The front half was turned down to 1.058" to fit inside the MRod diameter tube a total of 0.70", and mounting holes drilled and tapped for 8-32 screws top and bottom that will be 1/2" from the end of the tube.... This puts the rear trigger mounting hole 1.50" from the back of the adapter.... and that ends up in exactly the same place as the shoulder on the turned down version I made yesterday.... When assembled (without the tube) it looks like this....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Stock%20Assembly_zpsg0m5e7we.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Stock%20Assembly_zpsg0m5e7we.jpg.html)

With the stocks adjusted in the same holes, the LoP of both guns are the same, so they will share identical ergonomics.... I still have to make an insert for the straight through tube to mount the SSG and the rear of the trigger group.... and of course the SSG assemblies, but those will come much later when I have the valves and hammers made....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on December 05, 2017, 07:21:30 PM
Today I made the SSG adjusters.... In this style of SSG, the center stop rod is stationary (but adjustable) and a spring guide slides on it to compress the spring and then launch the hammer when you pull the trigger.... The adjusters were made from a 2" piece of 3/4" OD CRS, machined down to 5/8" for half the length and threaded 5/8"-28 TPI to match the inside of the SSG mounts.... The inside was drilled to 1/2" ID for 1.5" deep to provide a place for a longer than normal hammer spring.... The back part of the adjuster was drilled and tapped 1/4"-28 TPI for the adjustable stop rod.... With the adjuster screwed fully in, there is 2.5" available to the back of the hammer, and with it out all the way (about 3/4" of adjustment) I have enough room for a 3" hammer spring with no preload.... I have not yet made the spring guide which slides on the 1/4" stop bolt and propels the hammer.... Since both threads are the same pitch, you can hold the stop bolt with a screwdriver (you can see the slotted end in the photo) and adjust the outer sleeve to change the preload without changing the gap.... If you hold the outer adjuster, CW on the stop rod decreases the gap (and preload) and CCW increases the gap (and preload)....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Parts_zpsw9mauvcg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Parts_zpsw9mauvcg.jpg.html)

You can see that I have milled flats on the back of the adjuster, and I will be making a custom socket wrench to fit that.... Three sides are milled flat, 3/16" from the center, and you can make the initial adjustments with a 3/8" wrench.... One side is left unmachined, but is drilled and tapped for an 8-32 setscrew which will have small Delrin plug under it, pushing on the side of the 1/4"-28 threads as a brake.... There is a similar brake in the outer plug (the straight one for the one-piece tube is shown) to act as a brake for the 5/8"-28 threads on the adjuster.... These allow you to adjust the SSG preload and gap, but insure that the adjustments don't move on their own....

The stop rod shown was made from a 3" long bolt, and is too short to use with a 3" spring.... I will be making longer ones when I make the sliding spring guides....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on December 06, 2017, 01:43:21 PM
Today I made the wrench for adjusting the SSG through the end of the main tube.... The wrench consists of three parts, an extension tube, made from a leftover front piece of a Disco reservoir, a front end machined to fit onto the SSG Adjuster only one way, and a back end which mounts the handle and has a guide for the screwdriver....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench_zpsdrtdsn9f.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench_zpsdrtdsn9f.jpg.html)

The handle is simply a 3" long 1/4"-28 bolt, which will be locked in place with a locknut.... It is threaded into the rear mount, which is drilled 1/4" ID and turned to fit into the Disco tube.... The front end (lower left) is turned from a piece of 1" aluminum, with a 15/16" OD to fit through the back of the buffer tube, which I drilled out for that purpose.... It is also drilled through 1/4" for the screwdriver, and to allow the threaded stop rod to enter it, because it sticks out past the end of the SSG adjuster (see bottom right).... I milled a slot in the end of the wrench portion that is 3/8" wide, right out though one side, but blind on the other, where I used a 3/16" mill to create clearance in the corners.... That left a bump between which helps to center the tool on the end of the SSG adjuster.... It will only fit on one way.... The back of the wrench end is threaded 13/16"-28 to thread into the front of the Disco tube....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench%20Parts_zps4qkmsl28.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench%20Parts_zps4qkmsl28.jpg.html)

I used some Loctite 638 (green) to permanently install the front (wrench) end in the threads of the Disco tube, and then drilled the hole for the handle in the same plane as the slot, so that the bolt which serves as a handle points to the open end of the slot.... This corresponds to straight up in either gun, when the SSG adjuster is tightened in all the way, making it simple to count turns out from full in to determine the position of the adjuster....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/SSG%20Wrench%20Operation_zpsv6sqnhrh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/SSG%20Wrench%20Operation_zpsv6sqnhrh.jpg.html)

A long slotted screwdriver fits through the center of the wrench to engage the slot in the end of the stop rod.... This allow you to hold the rod and turn the adjuster (adjusting preload but not gap), to hold the adjuster and turn the stop rod (increasing or decreasing both), or without using the screwdriver simply turn the adjuster which moves the rod in as well (adjusting gap but not preload).... The bolt handle just clears the back of the tubes when the adjuster is all the way in, so all you have to do is slide off the stock to adjust the SSG....

Bob
Title: Re: Any Interest in 6mm ?
Post by: rsterne on December 06, 2017, 06:22:21 PM
This afternoon I made the spring guides and longer stop rods.... The guides were turned from Delrin rod, and are 0.35" OD x 1.5" long where they fit inside the spring and 0.59" OD on the flange, which is 1/8" thick.... They were drilled out with an "F" drill (0.257") so that they slide easily on the 1/4" rod.... There is a # 010 O-ring between the flange and the stop on the rod to act as a buffer.... The stop rods were made from a 4" long piece of 1/4" drill rod, threaded 1/4"-28 TPI for 1.5" of length to provide lots of adjustment.... The other end was also threaded 1/4"-28, and a nut bottomed in the threads, tightened down with Loctite 638 (green) to glue them permanently in place.... The nut was then turned down to 0.40" OD and contoured to the same shape as the bottom of the 7/16" drilled hole which will be drilled in the hammer.... The flange on the spring guide is what allows the hammer to compress the spring, and transmits the spring force to the hammer on firing....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Spring%20Guide%20and%20Longer%20Rod_zps8a3kpkm9.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Spring%20Guide%20and%20Longer%20Rod_zps8a3kpkm9.jpg.html)

This style of SSG has a couple of advantages.... First, it can be adjusted from the back without disassembly to change the preload like some of my earlier ones.... Secondly, other than the hammer, the only weight which is being accelerated by the spring is the very light Delrin guide, so little energy is lost.... The top assembly in the photo above is adjusted so that there is no preload on the 3" spring, and the distance between the flange on the guide and the mounting block is 1", which will be the maximum cocking distance I will build into these guns.... As you increase the preload, the slotted end of the stop rod will protrude more from the back of the SSG adjuster.... I have enough thread to allow nearly 1" of preload, which is more than I will ever use.... 3/8" preload on the 14 lb/in spring shown works out to 5 lbs.... If I run out of preload it is a simple matter to add a shim to the end of the spring inside the adjuster.... I'm very happy with how the SSG part of this project has turned out, next step is to think about the design of the hammer and make those....

Bob
Title: Re: Any Interest in 6mm ?
Post by: Christopher on December 07, 2017, 02:52:34 AM
Everything seems to be coming along nicely.  Keep the post coming. I really enjoy your build-along threads and this one is no exception. One may not really think about all the little parts that make a platform like this function, until you have to make every single one :o......time, time, and more time :)

Thanks,
Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: sixshootertexan on December 07, 2017, 09:40:10 AM
Didn't realize this thread turned into a build thread. Looking good Bob.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 07, 2017, 06:32:52 PM
I worked on the PRod trigger groups today.... Lloyd Sikes of AirGunLab makes taller sears so that the PRod pistol grip style trigger can be used with the thicker tube of an MRod.... The sear is about 0.030" taller, to make up for the 0.095" wall compared to the 0.0.65" wall of the PRod.... Lloyd's taller sear is on the left....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tall%20Sear_zpsdejvskyl.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tall%20Sear_zpsdejvskyl.jpg.html)

It is made from hardened steel, and extremely well made.... On the 6mm bottle gun, which uses a 0.095" wall tube, all I needed to do was install it in place of the stock one.... The straight tube I will be using on the .257 is 0.120" thick wall, however, so even the tall sear would be too short.... Fortunately, I had a solution.... The first gun I made with a PRod trigger group on a 0.095" wall tube (my Monocoque .257) I didn't have a tall sear, so I machined the top of the trigger group instead.... For the 0.120" wall, I simply did both....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Trigger%20Group_zpslfjjiaef.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Trigger%20Group_zpslfjjiaef.jpg.html)

The radius on the top of the PRod trigger group is intended for a 7/8" tube OD.... When used on a 1.25" OD tube, the center of the arc doesn't touch, only the sides of the groove bear against the tube, and there is about a 1/32" gap in the middle because of the mismatch of the radii.... Using a 1-1/4" router bit (shown) I milled the groove out to a larger radius, removing metal from both sides of the top of the trigger group until the bit JUST touched the center of the hollow.... This eliminated the gap in the center of the groove when bolted to a 1.25" OD tube, and moves the trigger group up 1/32".... By using the tall sear, and machining the trigger, it works perfectly on a 0.120" (even a 0.130" wall tube)....

I'm getting closer to working on the hammers....

Bob

Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 08, 2017, 07:33:14 PM
I made my first hammer today.... I wanted to make these builds with a separate cocking handle, but I knew the hammer had to be longer than normal and was concerned that they would be too heavy.... I decided that the only way to find out was to make one and weigh it....

I started out with a 5/8" diameter steel core 2" long that was drilled in 1-1/4" deep with a 7/16" drill.... It had to clear the stop rod and allow for 1" of travel, which I hope to achieve.... I knurled the outside and took a piece of 1-1/8" diameter MDS from Rocker1 (thanks David) and drilled it out 5/8" and pressed it on so that there was a socket for the flange of the spring guide to fit into (it is less than 5/8" OD).... I turned the back end to length, leaving just over 1/8" of the MDS protruding past the steel.... The Delrin spring guide will push directly on the steel core, while the MDS outer will prevent the sear from popping up behind the hammer.... This is the rear view of the hammer....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Hammer%20Rear_zpsp3kq4ear.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Hammer%20Rear_zpsp3kq4ear.jpg.html)

The MDS was turned to 1.2" long from the back to the lower corner where the sear engages.... If that proves to be too long to cock, then I will either move the sear location on the hammer back, or machine a bit off the front of the SSG mount, there is a bit available there in front of the screw locations.... The front of the hammer is just the steel core, and the overall length is 1.70", which is about 1/2" longer than an MRod hammer.... This leaves enough material between the front of the hole and the front of the hammer for a cocking handle to be installed.... The handle was made from a piece of 7/32" drill rod that is 1.7" long.... Both ends are turned down to 3/16" for 0.40" length, and threaded 10-32, leaving a shoulder 0.40" from each end.... The hammer is drilled 1.50" from the back, through and tapped to 10-32, and counterbored 7/32" to a depth of 1/8" so that the shouldered rod bottoms below flush.... The knob on the handle was made from a piece of 1/2" OD black Delrin rod 1" long.... It was drilled 5/32" to 0.8" deep and counterbored 7/32" for a depth of 0.30".... and then the lower portion tapped 10-32.... This allows it to thread into the Delrin handle, which gets its strength from the steel rod, but keeps the weigh down.... I usually use a piece of aluminum for the knob, and 1/4" steel for the shaft, but wanted a lighter approach.... Here is the front view of the hammer and cocking handle....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Hammer%20Front_zps7fbtqj35.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Hammer%20Front_zps7fbtqj35.jpg.html)

The last step was to mill two 3/8" long slots in the sides of the MDS to allow the hammer to vent during firing, to make sure there is no pressure buildup on the front, or vacuum on the back.... The total weight of the hammer and cocking handle is only 58.7 grams, only about 10% heavier than the Steel and MDS hammer I use successfully on my BRods.... I have two other hammers for the BRods, an all steel at 104 grams, and an MDS with aluminum core at only 27 grams.... so I can go lighter or heavier should the need arise....

This hammer is made for the 6mm bottle gun, I need to make the other one smaller in diameter to fit the thicker wall tube.... After making this, I have one concern, and that is the slots milled in the sides allowing the hammer to cock sideways in the tube more easily, since the cocking force is on the right side, and aligned with the slots.... When I make the second hammer for the .257, which will be running higher pressure, I won't be quite as concerned about weight, so I plan two changes.... The MDS will be full length, with a notch milled in the bottom for the sear.... and it will have a single vent slot in the top only.... This will leave both sides circular, in case there is any tendency to cock sideways and bind when cocking with this hammer.... That way I can determine if there is any difference, and which is better....

Bob


Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 09, 2017, 06:00:22 PM
I made the second hammer today, for the .257, which has a slightly smaller tube ID.... The lengths are all the same as the hammer I made yesterday, and I have both in the photos for comparision.... Here is the top view....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Top_zpsxnhicdqt.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Top_zpsxnhicdqt.jpg.html)

Note that I moved only used one vent groove, on the top instead of the sides, so the hammer has more bearing area to resist any binding in the tube due to the side cocking handle.... In addition, I made the MDS full length instead of stopping it behind the cocking handle.... Here is the bottom view....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Bottom_zpsje7uvaxg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Bottom_zpsje7uvaxg.jpg.html)

Instead of turning a 20 deg. bevel where the sear catches, I milled a flat to clear the sear and then milled the catch point on a 20 deg. angle to match the sear.... The new hammer is less than 2 grams heavier, and I like the appearance better, it looks like it should resist binding in the tube better than the first version with the shorter bearing length.... It's not worth changing the first one unless there is a problem, and having the two different versions will tell me if there is an issue with binding when cocking....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 10, 2017, 12:12:48 PM
Well today it finally starts to look a little bit like a gun.... and I got to find out that the hammer works as designed.... I measured two (dozen) times and then laid out and milled the cocking slot in the right side of the tube.... Here is what the long tube (intended for the tethered .257 cal) looks like now....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Long%20Tube%20with%20Hammer%20Slot_zps8lzf7fwt.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Long%20Tube%20with%20Hammer%20Slot_zps8lzf7fwt.jpg.html)

The hammer cocks and still has a bit of leeway for rearward movement before it hits the SSG mounting block that mounts the rear of the trigger.... When adjusted for 1.0" of hammer stroke, the front of the cocking handle rod is nearly 1/4" from the front of the slot when uncocked (as in the photo), so if I have the valve stem protruding 0.20" from the back of the valve (limiting the maximum lift to that, which is plenty).... and the stem touching the hammer when set for that 1" of stroke.... the hammer will hit the back of the valve body before the cocking handle hits the front of the slot.... which is what I wanted.... The hammer cocks smoothly and with relatively low effort with the 14 lb/in spring installed and about 5 lbs. of preload....

Now to lay out and machine the shorter tube for the regulated 6mm version to the same stage of completion....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 10, 2017, 02:07:19 PM
I got the trigger mounted on the short (regulated) tube, and milled the slots for the sear and cocking handle this afternoon.... This hammer works well also and I milled both the cocking slots 0.050" longer at the front.... With the handle at the front of the slot, you can see the back of the sear flush with the back of the hammer, so that is absolutely as far forward (maximum stoke) as I can go.... It is critical that the back of the hammer keeps the PRod sear pressed down, if it could pop up behind the hammer, the hammer would jam the valve open and dump the reservoir, and likely damage the hammer (or trigger) as well.... The length of the top face of the sear (about 1/8") is my safety margin....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Short%20Tube%20with%20Hammer%20Slot_zpsnwa0npva.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Short%20Tube%20with%20Hammer%20Slot_zpsnwa0npva.jpg.html)

This completes the stock, SSG and hammer assemblies on both guns.... Once I make a decision on the valves I will know where to mount them, and only after that can I proceed with the receivers.... Until I know where the valve exhaust port will be I can't make those.... The next steps will be making the front plug with fill fitting for the unregulated tube and the reversed tank block for the regulated one....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 11, 2017, 03:08:35 PM
I made the front plug and fill fitting for the long tube today....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Fill%20Fitting_zps9r1dulnx.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Fill%20Fitting_zps9r1dulnx.jpg.html)

It is a piece of 1" diameter 2024-T3 that is 1.4" long.... It is drilled through 1/8" for an air passage, and then drilled and tapped for four 10-32 x 1/4" long SHCSs with the head in shear to take the loads.... There is a single O-ring groove for a #117 O-ring.... The front is drilled and tapped 1/8"-27 NPT for a male Foster, and the back is drilled out a short distance to 5/8" just to gain back part of the volume lost to the plug.... I drilled the four 5/16" retaining holes in the tube at a 45 deg. angle to the vertical, so that the front plug can be removed without removing the barrel....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Reservoir%20End_zpsysjwtdvm.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Reservoir%20End_zpsysjwtdvm.jpg.html)

I'm quite pleased with this, the next job is to ponder how to make the reversed tank block for the short tube to hold my 500 cc Carbon Fibre bottle under the tube....

Bob

Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on December 11, 2017, 04:53:17 PM
Nice job on the end plug....Just out of curiosity, why did you decide to pin the plug instead of thread it? Any particular advantage or other reasons? Good forward thinking on making the screws accessible.... 8)

Thanks,
Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 11, 2017, 05:00:28 PM
Yes, the headstock bore on my lathe is only 3/4", so I can't pass a 1.25" tube though it to single-point thread it.... and the 36" bed of the lathe is not long enough to use a steady rest on the 39" tube and still get to the end to thread it.... That meant I would have had to use a tap, which I don't have.... Pinning the plug like I did is plenty strong enough (3 screws would have done it), and much easier for me to do....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on December 12, 2017, 04:35:30 AM
I won't speak for Bob, but I'd bet it is much stronger!
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 12, 2017, 08:30:28 AM
Threads and pinning can both have equal strength.... certainly sufficient to provide greater strength than the tube itself if desired.... Proper design is the key.... My preference is to have the weakest link in the chain the bearing load of the screw-heads in the sockets in the tube.... so that if a failure is imminent, those holes will show distortion before anything catastrophic occurs.... That is something that can't be done with threads, the weakest point is almost always just inboard of the threads, but outboard of the O-ring.... because the most common method of failure with a threaded end plug is pulling the entire assembly from the end of the tube outboard of the O-ring.... where the thread has reduced the wall thickness of the tube....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 12, 2017, 08:09:41 PM
Today I tackled the job I hate the most, but possibly the most satisfying if it turns out well.... I turned the stub and rear face of the tank block.... The piece I started with was a 1-1/4 x 3-1/2" piece of 6061-T6 rectangular bar stock.... I roughed out the stub material with my power hacksaw (finished with a hand saw) and then cut a piece 2-3/4" long, ending up with an "L" shaped piece of aluminum.... The small part of the "L" is for the round stub that inserts into the front of the tube, so I had to mount it in the lathe to make that round and the correct diameter, and cut the O-ring groove.... In the same operation, you face the rear surface of the block flat square to the stub.... The trick was mounting it in my lathe....

I have a 4-jaw chuck, with reversible jaws, but with them in the normal orientation one jaw was right out past the chuck face, because the block has to be offset so that the round stub is at one end.... I reversed that jaw, which solved that problem, but then the block has to sit on top of the first ledge on the jaw, and I didn't like the idea of trying to shim the block at the other end, there is incredible load when turning this piece, and it must be very rigidly mounted.... or it could jar loose and come flying out of the lathe, or break something (and maybe me).... I came up with the idea of reversing the opposite jaw as well, so that the block would sit on both of them, but NOT reverse the side jaws, so that they had more clamping area.... it worked perfectly, as you can see below.... Top and bottom jaws reversed, side jaws "normal"....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Turning%20the%20Tank%20Block_zpsex2kaxmr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Turning%20the%20Tank%20Block_zpsex2kaxmr.jpg.html)

Before putting the block in the chuck, I laid out and drilled a center hole for the stub, using a 60* center drill.... The by using a 60* center in the tail stock, pressing the block against the two reversed chuck jaws, it was pretty simple to get it centered.... I have never turned such a large, offset block before, and the impact with the tool bit is considerable if you take too big a bite.... so I used the slowest feed rate (0.004") and could only remove 0.005" per pass off the flat surface beside the stub.... I had left the material 1/10" oversize, so that took 20 passes at over 3 min. each.... well over an hour just to machine that flat surface.... Then I had to turn the 1-1/4" square stub that was sticking out to a 1.05" circular one, drill the center air passage (1/8") and cut the O-ring groove.... Between the setup and machining, it took all afternoon, and some of the evening.... I must be the world's  ~ s l o w e s t ~  machinist....  ::)

It was pretty nerve-wracking, so I will have a good sleep and tackle the rest of the block tomorrow....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 13, 2017, 10:32:44 PM
I finished the tank block today.... My 300 bar, 500cc Carbon Fibre tank clears the main tube by just over 1/16" when installed.... Here is the side view, showing the regulator installed....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Side_zpsemhjmm6q.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Side_zpsemhjmm6q.jpg.html)

The notch on the top front is for a barrel band, there are two 6-32 holes drilled and tapped on the front face to attach it.... As you can see, there is a Picatinny rail on the bottom.... The hole there is for the plug for the vertical air passage.... The plug is a low-profile 10-32 SHCS with a # 008 O-ring under the head in the milled 5/16" recess.... There are four 10-32 screws to retain the stub of the tank block in the tube, again drilled at a 45 deg. angle so that the tank block can be removed without removing the barrel.... The stub seals into the tube with a single # 118 O-ring.... The 1/8"-27 NPT tapped hole in the side is for a gauge for the pressure downstream of the regulator.... Below is the rear view....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Rear_zpscwzynwit.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Rear_zpscwzynwit.jpg.html)

The method of mounting the regulator is different from common practice.... Instead of using the two (red) O-rings inboard of the threads in a bored hole, the hole in the block is simply drilled deep enough to clear the length of the regulator and tapped 1/2"-14 NPS.... At the top of the hole is a recess milled with a 7/8" end mill to a depth of 0.085" to accept a # 115 O-ring.... This is a snug fit over the regulator, in the groove between the threads and the shoulder on the bonnet, which is 0.900" OD.... When the regulator is tightened into place, that O-ring fits into the groove in the tank block, and seals the regulator outboard of the threads.... This trick, pioneered by Travis, is much easier to machine, and is used on the Flex and Cobra.... Qudos to him and Jim Gaska for coming up with the idea.... The three 5/8" wide grooves milled around the middle of the tank block and the back and sides are only to remove a bit of weight, and pretty it up a bit.... Even so, the block weighs a hefty 8 ozs....  ::)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on December 14, 2017, 03:10:16 AM
Looking real nice. When you machine out your o-ring grooves, like for the #118 where your plenum tube will go, do you have a "rule of thumb" as to how wide and how deep you machine the groove in comparison to the o-ring? For example, the nominal thickness of a #118 is 3/32", or .094 (nominally), so how wide and deep do you go to ensure a good seal? Great work!

Thanks,
Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Nvreloader on December 14, 2017, 08:07:16 AM
Very nice and interesting machining tricks you used.........  8) I am still following along, and learning from you,
I for one greatly appreciate your info,photo's you pass along. 
Thank you, Bob.

Tia,
Don
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 14, 2017, 08:58:11 AM
HI Chris....

There are lots of sites that give O-ring gland dimensions, either in formula form, or tables.... For a 100 series (3/32" CS) O-ring, which are actually 0.103" nominal, the tables say 0.081-0.085" gland depth for static seals, which is 0.020" compression.... Dynamic (sliding) seals have a bit less compression (deeper glands).... The recommended groove width is 0.144", but I usually cut mine with a 1/8" tool, as there is still enough volume in the groove for the "squashed" O-ring at that width.... It is important to measure the gland depth from the TUBE ID that the O-ring is going to seal in, NOT the valve OD, which is smaller, often by about 0.010".... For the tube on my 6mm, the tubing ID is 1.062", so at 0.081" gland depth that means the groove ID is (1.062 - 2x0.081) = 1.062 - 0.162 = 0.900".... If the gland depth was 0.085", the groove diameter would be 0.892".... The grooves on an MRod valve are 0.895" on the ones I have here with roughly the same tube ID, maybe a couple of thou smaller....

Deeper grooves are easier to assemble (eg. when sliding the O-ring past the valve screw holes).... but more prone to leaking.... Harder O-rings, eg. 90D instead of 70D seem to be a bit easier to guide past a hole without damage, but on the other hand are harder to get started in the end of the tube without a good taper there.... IMO a 90D O-ring in a 0.085" gland depth "feels" like a 70D O-ring in a 0.081" gland depth when starting it into the tube.... because the 70D compresses easier.... 90D O-rings resist extrusion into the gap between the valve and tube at a higher pressure than a 70D.... although to be truthful I have never seen a problem with extrusion, even with a 70D O-ring into a 0.005" gap at 3,000 psi.... which is too big a gap according to the tables....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: sixshootertexan on December 14, 2017, 09:59:51 PM
You can just Google Parker oring handbook and download a pdf of it.

Looks good Bob. Wish I had known about the oring trick before I sent my lower to get anodized. Would have been a nice backup to the other 2 orings. I wanted to put a down stream gauge on mine but just didn't have the room.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 15, 2017, 09:21:34 AM
The hardest thing about making female ASA fittings is that 0.696" bored hole inside the threads for the O-rings to seal on.... sometimes I get away with cutting it with an 11/16" end mill, and sometimes it leaks (or is too small).... plus it is difficult to thread to the shoulder it creates (I actually made a bottoming tap to do that previously).... It was a brilliant solution WAR came up with to eliminate that seal and just seal at the outer end of the threads against the bonnet.... They use a 15/16" O-ring but I didn't have that size end mill, but I found that a # 115 O-ring had to be stretched a bit to fit on the regulator bonnet in the groove between the threads and the shoulder, so I went with that.... You just drill a 47/64" hole 0.70" deep and then tap it with a 1/2"-14 NPS tap.... mill a 0.085" deep recess for the O-ring with a 7/8" mill and it's done....  8)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 21, 2017, 04:43:19 PM
A couple of days ago I got a start on one of the valves.... got it roughed out, made some parts for the inside, and then spent a day finishing off the design.... Today I finished the first valve.... Here is the inside roughed out.... The valve is 5/8" ID with a 5/16" throat and a 1/8" stem....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Inside_zpsjwxaybsx.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Inside_zpsjwxaybsx.jpg.html)

The spring retainer end cap is a vented wheel that fits into a recess in the front of the valve and is retained by an circlip.... The area for the wheel is 3/4" ID.... I made the 3/8" thick and machined out the inside, leaving a 1/8" vented web.... That was my solution to the difficulty of holding a 1/8" thick part for machining....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Recess_zpses2sejxn.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Recess_zpses2sejxn.jpg.html)

Here is a front view of the completed valve.... The two long 6-32 screws are the front mounting bolts for the receiver.... They penetrate the valve BEHIND the valve seat, straddling the throat, which allows me to use larger screws than an MRod valve and yet have a larger ID....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Front_zpstx1ikiwq.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Front_zpstx1ikiwq.jpg.html)

The O-ring is located behind the recess for the wheel, where the valve wall is full thickness.... The gauge is tapped directly into the left side of the valve, behind the O-ring, so no need to drag it across a large hole in the tube.... Here is the back view, showing the huge 0.257" port, which is on a 30 deg. angle towards the 5/16" throat for improved flow....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Valve%20Back_zps0vagpjcu.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Valve%20Back_zps0vagpjcu.jpg.html)

The four valve mounting bolts are 10-32 x 1/4" SHCSs set down with the heads in shear.... They are in staggered pairs, the top and bottom pair in a similar location to an MRod valve, but the ones on the sides are 1/4" further forward.... I had to do that to make sure there was enough tube material for proper strength on the RH screw, which sits ahead of the cocking slot for the hammer.... The slot ends exactly at the back edge of the valve body....

The reason for no photos of the inside is that this valve is my own home-made version of the ART/SS valve.... Since I was privy to the development of it, I was able to design and make my own version.... but out of respect for Travis, I am not divulging the details until he gets his patent in place.... My sincere thanks to Lloyd and Travis for their help while I was making the very intricate guts for these valves.... I made several versions before I managed to get any parts that were even usable, they are, to say the least, challenging.... and well worth their price, IMO....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on December 21, 2017, 04:53:41 PM
WWOOOWW Bob! Awesome machining skills.  I figured you were up to something intricate since you hadn't updated the build in a few days. Looks like it all came together nicely.  I like the fourth screw, integrated gauge and the beefier breech screws, not to mention that it's a balanced valve as well.... 8)

Great job,
Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 21, 2017, 06:23:15 PM
Man o man that is a bit of work! The hours of time and R&D will pay off in the end I’m sure: This will be fun to watch.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 21, 2017, 06:36:16 PM
My first ART/SS valve.... it better work, I've bet the farm (these two guns) that it will....   :o .... It would be almost impossible to get enough hammer strike for a conventional valve of these dimensions at the operating pressures I intend, within the space I have for the hammer.... unless I can find a Gorilla to cock it.... ::)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 21, 2017, 06:57:41 PM
My first ART/SS valve.... it better work, I've bet the farm (these two guns) that it will....   :o .... It would be almost impossible to get enough hammer strike for a conventional valve of these dimensions at the operating pressures I intend, within the space I have for the hammer.... unless I can find a Gorilla to cock it.... ::)

Bob

 I have a feeling you will be just fine ;)
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: sixshootertexan on December 21, 2017, 09:57:35 PM
Nicely done Bob. Hope it shoots well with that valve.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 22, 2017, 07:09:53 PM
Today I drilled all the holes for the valve in the long (unregulated) tube.... Here is the right side....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Right%20Side_zpskqpudz7a.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Right%20Side_zpskqpudz7a.jpg.html)

You can see the cocking slot for the hammer, and now you can see why I moved the side valve mounting holes forward, to give lots of material between it and the front of the slot.... here is the left side....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Left%20Side_zps0reyye4s.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Left%20Side_zps0reyye4s.jpg.html)

You can see the large hole for the gauge on the side.... I installed the valve, hammer, SSG assembly and trigger group today and tested everything.... With the hammer set for 1" of travel I still have 0.22" between the front of the hammer and the back of the valve, and about 1/16" between the cocking handle and the front of the slot.... This allows for 0.20" of maximum lift and still have a 0.020" gap for the SSG.... The valves have an internal travel of about 0.24", so with the stem protruding 0.20" the hammer will hit the back of the valve before anything else hits and gets damaged.... I also made the second valve body today....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Two%20Valves_zpsiuyalz6k.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Two%20Valves_zpsiuyalz6k.jpg.html)

The one in the foreground is for the shorter regulated tube.... Since there is a gauge downstream of the regulator in the tank block, there is no hole in the side of the valve for a gauge like there is in the valve for the unregulated tube in the back.... The valve in the front is also larger in diameter because the regulated tube is 0.095" wall instead of 0.120" wall....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 22, 2017, 08:44:37 PM
 God thats a ton of work. Id have to charge 3k for a custom build like that maybe more.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on December 23, 2017, 03:03:36 AM
Those who can are justly proud. Those who can't are at least jealous, if not envious. Guess which group I'm in?!
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 23, 2017, 08:23:47 AM
The problem, Travis, as I'm sure I don't have to tell you, is that for every hour I spend machining, I spend a couple of hours thinking about the design and sitting at the computer doing and revising the drawings.... even though I did the basic design work during the summer, when I had no opportunity to work in the shop.... so I could start ordering the parts and materials....

A complete custom build like this is a challenge, but the satisfaction I get from seeing each piece fit and function the way it should replaces the toil with a sense of accomplishment.... so yes, I am very proud of it.... There are always things I know I could have done differently, or better.... but each of those experiences adds to my knowledge and hopefully improves the next project....

Long live projects....  8)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 23, 2017, 07:12:15 PM
Last day in the shop before Christmas.... I tidied up all the loose ends.... no photos because there was nothing new, just a second batch of what I have already made.... I built all the internals for my second ART/SS valve (my version), and drilled the holes in the short (regulated) tube to mount the valve.... Other than cut that tube to length (after I get the regulator for my 500 cc CF tank) and drill the 4 holes to retain the tank block, both "lowers" are now pretty much finished.... I am waiting for some 70D O-rings, once they arrive I will be able to assemble and pressure test them.... Oh, I forgot I still have to lap the valve seats and make sure the poppet face is square....

I finalized the design for the receivers today.... The material I bought wasn't tall enough to allow for slope in the scope dovetail, but fortunately I have enough 1 x 1.5" aluminum bar stock for the two receivers.... The scope rail will be angled 20 MOA to put the scope pretty much on optical center with a POA of 100 yards.... These are both single-shot guns, and I wanted to make both receivers identical and yet set one up for 6mm and the other for .257.... I plan to use an "L" shaped insert in the loading area, sized for each caliber, that will bolt into place.... The left hand wall of the receiver will be full height to increase rigidity, the bullet will load from the right, like on my Monocoque.... at least that's the plan at the moment....

I want to wish all my friends here on the Forums all the best for a Merry Christmas and a Happy New Year....  8)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Nvreloader on December 24, 2017, 09:16:10 AM
Bob

Thank you for ALL you have done for ALL of us, You have set the bar very high,
very few can even see to that level.

May you and yours have a very Happy and Merry Holidays,

Your friend,
Don
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 26, 2017, 07:03:19 PM
 When are your valve orings going to show up?
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 26, 2017, 08:33:14 PM
Maybe tomorrow.... I guess the return spring has to be strong enough to move the poppet, to allow it to close to fill?....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 26, 2017, 10:23:30 PM
Maybe tomorrow.... I guess the return spring has to be strong enough to move the poppet, to allow it to close to fill?....

Bob
Yes. doest take much also Krytox on the orings is highly recommended.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on December 27, 2017, 08:52:46 AM
I have some Dow 55 O-ring lube I use on all O-rings.... should be OK?.... Never seen Krytox around here....

How heavy a spring do you use?.... like a ball-point pen spring or heavier?....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on December 27, 2017, 06:20:42 PM
1lb
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on January 02, 2018, 07:03:00 PM
 Dont make me drive up there and finish this thing for you!!!
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on January 02, 2018, 07:37:04 PM
Assembled the .257 (unregulated) tube and at 4200 psi blew the poppet apart.... the large O-ring broke off the side of the gland.... I have to redesign the poppet and make a new, stronger one.... The good news is that it would open with dropping a 60 gram hammer down the tube 10" (no spring)....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: oldpro on January 02, 2018, 09:07:04 PM
Assembled the .257 (unregulated) tube and at 4200 psi blew the poppet apart.... the large O-ring broke off the side of the gland.... I have to redesign the poppet and make a new, stronger one.... The good news is that it would open with dropping a 60 gram hammer down the tube 10" (no spring)....

Bob
Good news to people who understand the clamping force on a poppet at those pressures. What’s your thoughts on making it hold up? Steel piston with peek insert for piston face maybe?
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on January 03, 2018, 08:41:14 AM
I have been discussing it with Lloyd and we have been trying to analyze the mode of failure and the forces (did you get the photo I emailed you).... When we calculate the load at 4200 psi, and compare it to the shear strength of the Delrin at the bottom of the O-ring gland, we still have about a 2:1 safety margin to shear.... What Lloyd thinks is happening (and I agree) is that the load from the pressure on the O-ring is mostly near the outer edge of the gland.... Since the gland is only 0.060" from the edge of the poppet, that force is "levering" the gland, ie bending it at the base, and a tear starts at the bottom front of the gland, which then rips across the gland at that point.... The solution we came up with (I just need the time to make one) is to move the O-ring 1/16" further towards the throat (providing I have the room, which I think I do).... This will double the thickness of the side of the gland, greatly reducing its tendency to bend, and hopefully allowing it to live at over 4000 psi.... and increase the safety margin in shear to 4 or 5:1....

I looked at extending the brass front portion of the poppet aft and making the gland in that, and facing the back of it with Delrin as a seal.... The problem is that you have to have a 100% seal between the brass and Delrin, or the HPA would simply slide the Delrin back on the stem and it would leak.... I don't see how any method of "inserting" the Delrin would help.... The other solution is to make the entire poppet of steel (or brass on a steel stem) and then install an O-ringed Delrin seat in the valve.... something I would sooner avoid if possible....

My concern, of course, is that if this happened with a bullet loaded, the gun would fire it on its own.... It might not be lethal, because the air is venting through the tiny groove in the stem.... but I don't want to chance it.... I wish I had the ability to test the new poppet at about 8,000-10,000 psi, just to make sure it will stand that pressure without failure....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 07, 2018, 03:39:55 PM
I have been cleaning up some leftover projects for the last month while I have been waiting for some 1.2 mm CS O-rings to arrive for the poppet in my version of the ART/SS valve.... They finally got here and I made a new poppet which worked out great.... The smaller O-rings allowed a shallower groove, which I moved further down the poppet towards the seat and now it seals great and seems to function fine, even at 4200 psi.... It is holding air pretty well, losing less than 100 psi per day, which is good enough for now, and often slow leaks like this improve with time, as they are often the poppet on the seat.... Anyways, assuming it is good enough for now, the next order of business is to make the uppers, and then ream the chambers and mount the barrels.... After that I can shoot these guns for the first time, as I cast some bullets last week as well....

I started on the receivers yesterday, cut them to length (actually 1" over) and machined the concave bottom to fit against the tube on both receivers, which will be interchangeable on the lowers.... Today I laid out and center-drilled both ends of the bore for the barrel and bolt, high enough above the top of the tube to allow for the 20 mm OD barrel sleeve, plus 0.20" to allow for the thickness of a piece of 1-1/4" ABS pipe which I will be using for the foregrip on the unregulated .257 cal.... That plastic pipe is 0.150" wall, so it will just nicely clear the Carbon Fibre barrel sleeve.... It will be captured between a recess on the bottom of the receiver and the tube, like I did with the foregrip on the Monocoque.... Anyways, the C/L of the bore is 0.60" above the top of the main tube.... Once the locations were center-drilled, I mounted the receiver between centers on my lathe, and then held the back in my 4-jaw chuck.... Having it sit on a 60 deg. center inside the spindle bore allows easy centering of the jaws, you just tighten them progressively on the four side of the receiver until it is secure.... Using a live center (ie one that spins on a bearing) in the tailstock, I machined a 1" long collar on the front of the receivers (which is why I left them 1" too long).... The collars will ride in my steady-rest to support the receivers on center while I drill them full length....

I first drilled a 1/4" pilot hole from front to back, using a foot long 1/4" drill bit, stopping just before I hit the 60 deg. center in the headstock.... I then used a long 1/2" drill to increase the diameter to the finished size, removed the receiver from the lathe (so the 60 deg. center wasn't in the way, and drilled through the last 1/2" at the back.... The hole was straight and true, and parallel to the top of the tube in both planes, which is what I wanted.... A piece of 1/2" CRS slides perfectly through the receiver, full length, so I know that the bolt and the barrel will be aligned and parallel.... I them mounted the receiver back in the lathe between centers, re-checked the steady-rest position, and then drilled the front of the receiver out to 25/32" to accept the 20 mm CF barrel sleeve.... The sleeve is about 0.004" larger than the drill size, but it just starts into the hole, so all it will need is a bit of sanding to be a perfect slide fit....  Here is what it looks like at the moment.... I only have one drilled at the present time, the other one will be done tomorrow, all going well....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20257%20Receiver_zpslrskmram.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20257%20Receiver_zpslrskmram.jpg.html)

The plan is to cut off the collar, it was only there to allow me to support the front of the receiver in my steady-rest.... I don't need it for support, as the barrel sleeve goes 2.5" into the receiver, which is over 3 diameters.... It will be located by two sets of 3 setscrews at 120 deg. so the assembly should be 100% rigid when complete....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 08, 2018, 04:22:31 PM
I drilled the other receiver today, and then drilled and countersunk all the mounting holes and drilled through for the transfer port....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Two%20Receivers_zpsqhr7ndbr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Two%20Receivers_zpsqhr7ndbr.jpg.html)

The small recess on the bottom just behind the transfer port is to clear the upper valve mounting screw, which is just proud of the tube.... The receivers, like the tubes, are drilled on the same pattern, so the uppers will be interchangeable on the lowers.... Although I intend to build the .257 on the long, unregulated tube with the thick wall (4200 psi MSWP) and the 6 mm on the regulated bottle version with the short tube (thinner wall with 3200 psi MSWP).... the interchangeability will allow me to test the other way around, and change my mind should I decide to....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: grumpy on February 09, 2018, 04:46:43 AM
Definitely following this one. What molds do you plan on using for it Bob ?

Dave
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 09, 2018, 05:02:59 PM
I have three 6 mm moulds, Dave.... the 60 gr. 6mm Bowman from Arsenal (4 cavity with 2 HollowPointed by Erik).... the 74 gr. NOE.... and the shortened 64 gr. version of that.... both with Lyman HP pins in one cavity....

Today I milled out the loading port area in the two receivers.... Instead of milling it straight across, I left the left-hand side of the receiver intact from the boreline over, so that I don't lose so much rigidity.... These guns are single-shot, so no need to cut it away more than that.... I did this on my Monocoque and it works well, but of course you must load the bullet from the right side.... Drilling a 1/2" hole straight through the receiver to assure the alignment of the bolt and barrel means that when you machine the loading port you don't have a tray to guide the bullet into the bore.... so that is made from a separate piece of 1/2" diameter steel.... I drilled one for 6 mm and the other for .257 before milling them to shape.... You can see one of the inserts sitting on top of the receiver in the foreground.... along with a flat-head 4-40 screw which holds it in place.... The back receiver already has one installed....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Loading%20Ports_zps7qy8s6pr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Loading%20Ports_zps7qy8s6pr.jpg.html)

With the loading tray in place, the right side is level with the centerline of the bore.... and the left side is vertical, tangent to the left side of the bore.... You don't need to look at what you are doing to load, just place the bullet on the right hand lip of the tray, and roll it to the left and close the bolt....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on February 09, 2018, 05:27:51 PM
Nice to see you back on the 6mm build since you got your metric orings in.  Everything is looking real nice.

Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 11, 2018, 06:05:05 PM
I got lots more done on the receivers today.... This reduced the weight of them quite a bit.... and vastly improves the appearance....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Receivers%20Shaped_zpsqckw5end.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Receivers%20Shaped_zpsqckw5end.jpg.html)

The top and upper edges are now milled down, leaving raised areas where the dovetails for the scope mounts will be.... I also bevelled the top corners as well.... When I machine the dovetails I will be angling them down 20-25 MOA at the front to put the barrel on POA at 100 yards with the scope still optically centered....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 13, 2018, 06:31:17 PM
I worked on the receivers more today.... I drilled and tapped the six holes for the set-screws that will secure the barrel.... The original plan was for 10-32 screws at 120 deg. to each other.... but I was unable to get them of the proper length here in town, but I was able to get 5 mm x 0.8 mm Metric setscrews that are 10 mm long.... You can enlarge 10-32 threads to M5 by simply running the tap through them, as they are the same pitch (within less than 1%) and the Metric screws are 0.008" larger than the 10-32s.... I dislike mixing SAE and Metric fasteners on a project, but the alternative would have been to wait weeks to get the 10-32s.... I justified it by the fact that the barrels are 14 mm and the CF sleeve is 20 mm OD.... so at least everything to do with the barrels is Metric....  ::)

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/J%20Slots_zpsfqmsiviy.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/J%20Slots_zpsfqmsiviy.jpg.html)

I had one other little glitch when setting up to drill the lower holes for the setscrews.... In order for the receiver to clear the carriage on my lathe (I was using my milling attachment to drill and tap the holes accurately) I could not drill them 30 deg. below the horizontal, I had to use 35 deg.... This is of no practical importance, but means that the angle from the top to each side screw is 125 deg. and the angle between the bottom screws is 110 deg.... instead of them all being 120 deg....

I also set up and milled the slots for the bolt handle today.... The front receiver is finished, but dinner hit the table before I got the vertical part of the rear slot done.... I'll do that tomorrow before I set up to fly-cut the recess in the front bottom of the receivers to locate the plastic pipe of the forestock....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on February 14, 2018, 05:27:05 AM
I like the way you made the bolt cutout. The one on my Cobra allows the bolt to literally flop around, and seemingly always be in the wrong position for a quick shot. Maybe Jim Gaska will see this.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 14, 2018, 08:04:08 AM
Alan, the main reason for the "J-Slot" is to allow the bolt to be retracted completely out of the airflow to allow full bore-area porting throughout the airflow path.... There is an added benefit, which I have not 100% decided to take advantage of in these builds.... You can install a long pin with an adjusting screw at the back of the receiver, in line with the lower slot, to adjust how far the bolt face can be retracted.... This allows complete control over the velocity from maximum all the way down to about 200-300 fps (you can literally see the pellet in the air).... The further in you screw the adjuster, the smaller the barrel port....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on February 14, 2018, 11:13:26 AM
I do understand the reason. The Cobra has a "T" slot. Once you seat the pellet, you pull back slightly, and then down. The way the detent works, is, well, backward. The bolt should have a grove along its whole path, with a bridge and a deeper "pit" for the detent device. All of this, as a way to keep the bolt in place. Since it doesn't have this, I constantly have to reseat the position of the bolt before shooting as the bolt is just plan loose! I thought about finding a cabinet door, plunger-type keeper, but haven't found one small enough.

Just this morning, I finished up my 27 tin through the .25 caliber Cobra. The edges of the vertical part of the slot are now rounded off, making things worse. It is the only thing I don't like about its design. Or most other bolt air guns for that matter.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 14, 2018, 01:04:24 PM
Yes, many airguns need a slight recess in the back bottom of the vertical bolt slot so that the bolt doesn't pop up.... The only disadvantage of the J-slot is if you switch back and forth from a gun that doesn't have one, you can forget to pull back to clear the bolt nose from the barrel port.... and the result is a very weak shot....

Here are the receivers with everything now done except to machine the 20-25 MOA slope in the scope mounts and cut the dovetails in them....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Recess%20and%20Velocity%20Adjuster_zpss1zcdvxd.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Recess%20and%20Velocity%20Adjuster_zpss1zcdvxd.jpg.html)

On the lower front corner you can see the semi-circular recess milled to act as a clamp for the plastic pipe forestock.... It pinches the pipe between the bottom of the receiver and the main air tube, mounting it solidly at the back in the lowest possible position so that it doesn't rattle around, and clears the barrel.... The velocity adjusting screws are installed in the back, in line with the lower bolt slot.... The 8-32 SHCS pushes on a 1.5" long steel pin that can prevent the bolt handle from retracting fully in the slot.... I have about 10 turns of adjustment, the back receiver has the adjuster fully retracted (maximum velocity) and the one in front has the adjuster set to minimum velocity.... I labelled the steel pin which is sticking out into the lower bolt slot, which holds the bolt forward so that the nose obstructs the barrel port, reducing airflow (to almost zero when fully closed as shown).... You can't see it in these photos, but there is a vertical hole coming up from the bottom, in line with the bottom of the adjusting screw.... It is tapped for a 6-32 setscrew which presses on a 1/4" long piece of thin Teflon rod which acts as a brake to prevent the velocity adjusting screw from moving by itself....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on February 14, 2018, 02:22:49 PM
The screw is a good idea for more reasons than one. I often shoot inside the hay barn. As it is, I use my 397, and just 2 or three pumps to keep from shooting holes in the roof. Even then, a miss results in a dent. This "feature" would allow for that without retuning the pressure and/or hammer on my PCP.

I see things like this (mostly from you!), and I say to myself... "Why didn't someone else think of that?"
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 16, 2018, 04:12:24 PM
I got to work on the barrels today.... The first order of business was to machine the breech end to 1/2" OD for 1" of length so that it will fit into the receiver.... In addition, I had to machine down the OD of the carbon fibre tube slightly to fit inside the 25/32" forward section which is drilled to a depth of 2.5".... I did that with the end of the tube running on a live center in the tailstock of the lathe to insure concentricity between the ID and OD, and it worked out great.... Both the CF sleeve and the barrel slide perfectly into the receiver and can be rotated individually, showing they are concentric with each other and the holes in the receiver are as well.... This was a bit of a nervous time, as any inaccuracy there would have been hard to correct.... At the muzzle end I turned the barrel down to 1/2" as well and threaded it 1/2"-20 NF so that it can accept either a Hatsan Air Stripper (as a backup) or my intended Harmonic Tuner, which I have yet to make.... Here is a photo of the barrel ends, breech on top, muzzle below....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Barrel%20Ends_zpsdvgtnbvh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Barrel%20Ends_zpsdvgtnbvh.jpg.html)

and here is a photo of them with the CF sleeve in place (but not bonded yet)....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Sleeve%20Ends_zpsajbx6rsa.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Sleeve%20Ends_zpsajbx6rsa.jpg.html)

You can see where I had to skin down the outside of the CF tube to fit the 25/32" hole in the receiver, just a few thou was all that was required.... The next job will be to cut the chambers in the barrels before bonding on the CF sleeves.... I think the reamer I made for my .257 Monocoque will work, but I will have to make a new chamber reamer for the 6 mm.... I received some samples from Nick at Nielsen Specialty Ammo in the mail today (perfect timing, thanks Nick), as I would like to make sure the chamber in the .257 will accept as many different bullets as possible.... Here is a photo of the selection of .257 bullets I now have to try....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Bullets_zpsr8irkv1r.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Bullets_zpsr8irkv1r.jpg.html)

Left to Right they are.... My 98 gr. BBT HP, the 91 gr. Noble from Nick and his 85 gr. rebated boattail HP, an 88 gr. RCBS 82301, an 82 gr. NOE 260-80 FN, and a 73 gr. Lyman 257420.... I can also cast HP versions of the 82301 and 257420, so I will have lots of bullets to choose from.... I don't expect the 98 gr. BBT (or the FN version of it) to work in the 10" twist of the TJs barrel I have.... so if the chamber has to be too short to fit all the other bullets for it to chamber, so be it.... but just looking at the position of the ogives in the above photo, I think I can cut a chamber that will work with all of them.... If anything, the bullet with the Ogive starting the furthest forward is Nick's swaged HPBT.... Here are the 6mm Bullets.... the TJs barrel I have is also 10" twist....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Bullets_zpsovyvnprm.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Bullets_zpsovyvnprm.jpg.html)

Left to Right they are.... 58 gr. Bowman HP from Arsenal, 59 gr. NOE 245-64 HP and 69 gr. NOE 245-74 HP.... I can also cast FN versions of all three bullets.... The weights of the FN versions are 61 gr., 63 gr. and 73 gr. respectively.... The 63 gr. NOE is a shortened, FB version of the 73 gr. beside it, with the GC shank removed.... I also have a mould for a 65 gr. shortened version of the NOE 260-80, done the same way, but that will be too light for the power of this .257 cal (I hope)....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: grumpy on February 16, 2018, 05:18:36 PM
Never know about that 98gr in the 10" barrel. Lloyd  had pretty good accuracy with the 93gr in my .257 with a 10". Ironically, he tried the 100gr, and it was only so so. I want to try some a little heavier for giggles.

Even tho I hardly understand much of what you say, I follow along closely ! lol

Dave
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 16, 2018, 07:02:05 PM
Dave, the problem is that boattails make the bullet act like it is longer.... That's good for BC, but requires a faster twist for stability.... That 98 gr. BBT in theory needs about an 8" twist.... I designed a 90 gr. BBT, but no interest at NOE, so it has never even reached Group Buy status.... It's just a bit longer than Doug's 91 gr. and in theory needs a 9" twist... but I suspect it may well work in the 10" in this build.... I made the loading port 0.80" long to accommodate it....

(http://i378.photobucket.com/albums/oo221/rsterne/NOE%20Bobs%20Boattails/257-90-FN_BT__90_gr_Sketch_zpsmxzl1znq.jpg) (http://s378.photobucket.com/user/rsterne/media/NOE%20Bobs%20Boattails/257-90-FN_BT__90_gr_Sketch_zpsmxzl1znq.jpg.html)

The 78 gr. BBT is in Group Buy, but not enough guys so far....  http://noebulletmolds.com/smf/index.php/topic,1628.0.html

It would be nice to see that bullet made.... should be fine in an 11" twist, so the 10" is a no-brainer, at least in theory....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 17, 2018, 03:19:37 PM
I worked on making the Harmonic Tuners today.... I got two of the brass weights made, and one of the mounts that screws onto the muzzle.... Here is what it looks like when assembled....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Harmonic%20Tuner_zpsejrausfr.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Harmonic%20Tuner_zpsejrausfr.jpg.html)

The threads are 15/16"-28.... I like 28 TPI for this job because 10 deg. of rotation is 0.001" of movement (1 "hour" on a clock face is 0.003", 1 turn is 0.036").... The brass weight is made from a piece of 1.5" bar stock 1" long, the setscrew presses on a short piece of Teflon rod which acts as a brake to prevent the weight from moving by itself.... The mount is made from a piece of 1" CRS.... There is a small collar of that diameter at the front, with a 3/16" hole drilled though it to allow it to be tightened onto the muzzle with a short piece of 3/16" bar stock.... The remainder is threaded, the 2" of threads giving over 1" of adjustment for the weight.... The center portion is threaded inside 1/2"-20 NF to thread onto the barrel, and the back is counterbored 0.80" ID for 1" of length to fit over the CF sleeve.... The front is drilled out 3/4" ID, it only projects 1/2" past the muzzle to allow the HPA from the shot to escape quickly without affecting the bullet.... and it also serves to protect the crown which is a simple 90 deg. angle....

The mount weighs a couple of ounces, and the movable brass weight weighs just over 5 oz. at the present time, although I may put chamfers on the corners for appearance after initial testing.... I'm really looking forward to trying this system, I know it is tremendously successful in rimfire benchrest, where it can drastically affect the group size....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: sixshootertexan on February 17, 2018, 09:07:00 PM
I like the tuner.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 18, 2018, 04:02:56 PM
Here are the completed harmonic barrel tuners.... The muzzle of the barrel is about 3/8" inside the front of the mount, about where the outside threads start....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Harmonic%20Tuners%20With%20Scale_zpsenzsxvtc.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Harmonic%20Tuners%20With%20Scale_zpsenzsxvtc.jpg.html)

The scale is like a clock face, with the quarters having longer index marks.... with 12 o'clock being where the setscrew is.... Each mark equals 0.003" of movement on the tuning weight.... By starting with the weight against the shoulder at the front, you can record the position using "hours" for the turns and "minutes" for the index marks, so 9-1/3 turns I would record as 9:20.... and 15-3/4 turns as 15:45 etc.etc.... I'm really pleased with the way they turned out....

Bob

Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on February 18, 2018, 05:25:57 PM
That looks great. How did you tool the "clock" mark indicators on the adjuster?

Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 18, 2018, 06:14:42 PM
I held it in a 5C collet mounted in a Hex block in my milling attachment in the lathe, oriented so that the beveled edge of the weight was a 90 deg. to the axis of the lathe.... and used a 1/16" end mill (actually a tiny router bit) in the chuck.... I advanced the work towards the chuck in 0.005" increments, making two passes for a depth of 0.010" for the marks.... The crossfeed of the carriage governed the length of the marks.... The six faces of the hex block gave me half the marks, then I rotated the weight 90 deg. in the hex block and did the other six.... Sounds easy, but it took me all afternoon to do the 24 index marks....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 19, 2018, 12:46:39 PM
I cut the chamber in the .257 barrel today, using the reamer I made for my Monocoque....

(http://i378.photobucket.com/albums/oo221/rsterne/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg) (http://s378.photobucket.com/user/rsterne/media/257%20Benchrest%20PCP/257%20Monocoque%20Chamber%20Reamer_zpsj1ordmct.jpg.html)

Here are all the bullets that will fit.... They were all chambered to a depth of 0.60" from the end of the barrel, which will put the base just ahead of the front of the barrel port.... All bullets were sized to 0.257" before testing how they chambered.... When the chamber is too short, you sure know it, as you have to push hard enough to mark up the base, and it's pretty obvious when you get the length right....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Bullets_zpshef0w8ul.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Bullets_zpshef0w8ul.jpg.html)

I enhanced the contrast as much as possible so that you can see the rifling marks, but they are still hard to see on all except the longest two BBTs (112 gr. FN and 98 gr. HP), where they are clear on the back of the head.... The shortest bullet is the Lyman 257420 73 gr. and it barely touches the leade.... If you push it in by hand, you can only feel resistance for about the last 1/16", and basically cannot see any marks, even with a loupe, unless you push it in another 1/16", where you feel significant resistance.... I don't expect the two longest bullets to work in the 10" twist in this barrel.... but since I can chamber them I will be able to test that and prove or disprove the validity of the Kolbe Twist Calculator numbers for them.... Many of my BBTs seem to be stable in a slower twist than it gives, so there is a chance that the 98 gr. HP may work.... providing I have enough power to push it....

The other four bullets all slid in between 0.50-0.54" and then took a bit of a push (not much, mind you) to seat them to 0.60".... If you look carefully you can see shallow marks from the tapered leade, which they are sitting firmly against when chambered.... Those 4 bullets, from L to R, are the 91 gr. Noble, the 85 gr. NSA BTHP, the 88 gr. RCBS 82301, and the 82 gr. NOE 260-80 FN.... If I find one particular bullet shoots the best and want to play with different seating depths, I can do that by changing the length of the bolt nose....

Next step is to make the bolt, cut the O-ring groove and polish the chamber behind the barrel port.... then cut the CF sleeve to final length and glue it on.... and then machine the barrel port.... I was very pleased with the way the 3-flute reamer worked, so I am going to copy that design when I make the one for the 6mm barrel.... just smaller diameters for the pilot and chamber of course....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 19, 2018, 04:56:47 PM
I made the 6mm reamer this afternoon.... still not hardened and tempered but it turned out dimensionally accurate....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Reamer_zpsrojpc1lb.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Reamer_zpsrojpc1lb.jpg.html)

It is made from O1 Drill Rod.... The next step is to heat it to cherry red and quench it in oil to harden it.... Then I will polish it, hone the cutting edge again, and then temper it in the oven.... tomorrow's jobs....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 20, 2018, 04:33:36 PM
Here is what the finished reamer looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tempered%20Reamer_zps2bub7oat.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tempered%20Reamer_zps2bub7oat.jpg.html)

It was hardened, polished, and them tempered for 30 min. at 465*F, raising the temperature to 480*F for the last 5 minutes because it was a little too pale a straw colour.... The result is a nice brown, the way I like my reamers....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on February 20, 2018, 05:07:53 PM
Bob,
What is the diameter at the end of the reamer that would enter the barrel first (with no flutes)? Then how much taper do you have have on the fluted part?
BTW, great job on the reamer  8)

Thanks,
Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 20, 2018, 06:08:53 PM
The pilot is 0.232" and slides easily into the lands (which I measured at 0.234").... It then steps down to 0.220" and then a taper of 1 deg. per side starts from there.... That continues until it reaches the diameter of the grooves 0.243" (about in the middle of the flutes) and then continues back parallel at that diameter to cut the chamber.... It then steps down again to 0.220" for enough length allow you to feed the reamer deep enough to cut the chamber plus about 1/4".... The shank is simply the 3/8" drill rod I started with.... It is long enough to bottom in the Jacob's chuck in my tailstock, so that it can't slide back.... Both chucks have to be very tight to prevent the barrel, or the reamer, from slipping in them.... as the loads are very high.... If you feed too fast, you can weld the reamer into the barrel, and break it.... Don't ask how I know that....  :-[

You can actually see where the tapered leade stops and the straight chamber starts because of the lighting (a total fluke, from the flash).... The lighter blue reflection is on the taper, and where it stops is where the angle changes (only 1 deg.).... Behind that the reamer is straight.... The only part that actually does any cutting is about the last 3/16-1/4" of the taper, which cuts a taper in the rifling to form the leade in the barrel.... Ahead of that (over 3/4 of the tapered part) is smaller than the lands and doesn't touch anything.... The parallel section rubs along the chamber and polishes off any high spots, leaving it parallel, and hopefully the right diameter that a sized bullet just slides in until the nose hits the tapered leade.... It is critical to stop feeding the reamer at the right depth so that the bullet is seated against some part of the leade.... Too short a chamber and it is hard to close the bolt.... and too long a chamber and the bullet will not be against the leade, and get a "running start" before it engages the rifling.... There us usually about a 1/8" range of length of bullet that will fit any given chamber properly....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 21, 2018, 06:28:17 PM
It's always a nervous time when you first use a new chamber reamer.... They seem to get smaller through the polishing, hardening and repolishing, and I'l always wondering if it will cut the chamber to the right diameter.... When I set up to cut the chamber in my 6mm barrel today and starting advancing the reamer, it went so easy I thought "carp, it's too small".... I cut the leade into the barrel about 1/4", and then pulled it out.... To my surprise, and delight, I found that it cut better than any reamer I had ever made before, and the little channel between the flutes that I had filled with oil had a nice pile of shavings sitting in it....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Reamer%20Cutting%20Well_zpsfy9jj49s.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Reamer%20Cutting%20Well_zpsfy9jj49s.jpg.html)

Usually you can "feel" quite a bit of resistance on the handwheel on the tailstock as you feed the reamer in, the barrel gets warm, and the shavings are not much more than dust size.... Not so with this reamer, the shavings were like little needles, about 1/16" long and 0.005" in diameter or so.... I could actually feel the "bump-bump-bump" as each flute hit the rifling lands and slowly carved them away.... I don't know why this one is so much better.... but I hope they all come out like this from now on.... It may be that I honed it just right.... I know I will try the same honing technique on another reamer the next time, to see if that was the difference.... I sure hope so, this one cut a beautiful chamber in short order.... Here are the three 6mm bullets I used to set the length....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Chambered%20Bullets_zpsxkbhzazg.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Chambered%20Bullets_zpsxkbhzazg.jpg.html)

Left to Right are the 63 gr. NOE 245-64 FN.... the 61 gr. Bowman by Arsenal.... and the 73 gr. NOE 245-74 FN.... The 63 gr. is a shortened version of the 73 gr., with the gas check shank missing.... These two bullets are "bore riders", and you can see the shiny spots on the nose of the 73 gr. where it rubbed along the lands.... The front driving band is engraved to about half the rifling depth, as it is sitting in about the middle of the leade.... There are very slight marks on the rear band from the back of the leade, and about the same on the back band of the Bowman (which is a copy of the Lyman 257420, scaled down to 6mm).... The middle band of the Bowman is engraved about half depth, and the very front of the front band is just about full rifling depth, which is what I aim for.... The 63 gr. barely touches the leade with the front band, but if you push slowly on it, you can feel that it is seated firmly against it, but just enough to leave tiny marks.... There are some tiny polished spots on the nose, just at the back of the ogive, where it is just sitting on the lands.... I'm very pleased with the way this chamber came out.... In terms of size, a bullet sized to 0.243" slides in easily.... but one sized to 0.244" requires a bit of a push.... so the chamber size is perfect.... This reamer is a KEEPER !!!

This afternoon I set up the receivers in my milling attachment in the lathe, and adjusted it so that it cut a 20 MOA angle into the top of the Dovetails.... That works out to only about 1mm (0.040") less height at the front of the dovetail than at the rear.... but should put the POI at about optical center of the scope at 100 yards.... I then machined the dovetails into the sides of the raised portions on the receivers.... I took a bunch of photos of the two receivers with the dovetails, and had trouble with reflections hiding the angle of the dovetails.... but you can just about see that in the photo below (with a little imagination)....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Angled%20Dovetails_zpsm5txavkk.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Angled%20Dovetails_zpsm5txavkk.jpg.html)

If you look closely, you will see that at the front of the dovetail, the bottom of the cutter ran along the top edge of the bevel on the corners of the receiver.... but at the back of the dovetail the cutter left a ridge 1mm above the top of the bevel.... It's hard to believe that is all the elevation angle required of the barrel, relative to the scope, to put you on target at 100 yards.... but 0.040" in 6" works out to 24" at 100 yards (0.040 x 100 x 3 x 12/6).... When you mount the scope you can barely see the angle, if you didn't know it was there you would never notice it....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on February 21, 2018, 07:14:42 PM
Man, that looks super nice. Getting a little closer to putting some lead across the chrony.  Thumbs up on the reamer 8)

Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 26, 2018, 02:59:56 PM
Over the last 3 days I machined the O-ring groove in the breech of both barrels, and cut the CF sleeve to length and glued it onto the barrel liner with Loctite 638 (green).... After curing 24 hours, I gave it a post-cure in my wife's oven at 175*F for 3 hours.... This greatly enhances the strength of the bond.... Today I laid out and machined the barrel ports, and then installed each barrel in its receiver with a couple of setscrews (just tightened a bit against the CF sleeve), making sure the flat on the barrel port was perfectly centered in the hole in the receiver for the transfer port.... I made a drill jig from a 20mm long x M5 SHCS by drilling a 1/8" hole through it in the lathe.... and then inserted it in each of the holes in turn and drilled through the carbon fibre until I touched the steel of the barrel with the 1/8" drill bit.... I then mounted the barrel in my milling attachment in the lathe, centering off each 1/8" pilot hole, and enlarged the hole to clear the M5 setscrews with a #8 drill.... I drilled deep enough to leave a shallow pocket in the steel liner for each screw.... Here is the way that works....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Drilling%20Jig%20and%20Barrel%20Port_zps81wbc9mu.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Drilling%20Jig%20and%20Barrel%20Port_zps81wbc9mu.jpg.html)

The piece of tape on the drill bit was just a visual indicator to let me know when I would hit the steel.... The drilled out M5 SHCS worked perfectly as a drill guide, it is a great way to mark setscrew pockets accurately in a barrel.... I deburred the barrel ports and faired the 0.260" round transfer port seat ID into the oblong barrel port which had been machined with a 3/16" end mill.... The port in the 6 mm ended up at 0.194" wide by 0.294" long and the one in the .257 is 0.205" wide by 0.305" long.... which gives me full bore-area porting in both barrels.... Here is a photo of one of the finished barrels installed in the receiver....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Barrel%20Installation_zpsenxjy7t0.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Barrel%20Installation_zpsenxjy7t0.jpg.html)

The next job is to complete the bolts.... I already have them turned down to diameter, but have yet to install the bolt handles and cut
them to length at both ends.... The barrels also need lapping inside with JB's Bore Paste and polishing with Bore Brite.... I'm getting pretty close to being able to take the first shots....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on February 28, 2018, 05:56:28 PM
Final assembly and first shots today.... Yesterday I cut the bolts to length and drilled and tapped them for the bolt handles.... I checked the chambering of all the bullets, and the .257 was OK but the longest 6mm bullet (73 gr.) was too hard to chamber, so I had to shorten the front of the bolt about 0.050" until I could just chamber it.... I then sanded the receivers and cleaned them thoroughly, inside and out.... Today I lapped the bores with JBs Bore Paste and then polished them with Bore Brite.... I made the bolt handles, and cleaned and assembled the uppers for the first time.... Everything worked smoothly, so I measured the required length for the transfer port on  the unregulated gun (I'm still waiting for the regulator to finish the other lower).... It turns out the both the 6mm and .257 will require the same length transfer ports, which means I won't have to make multiples, just one for each lower.... The transfer ports are made from a piece of 3/8" OD Teflon rod, drilled out with a size "F" drill (0.257") and faced flat on the ends to the correct length to have about 0.020" of crush for sealing.... That was the last part required, so I was able to bolt the upper to the lower for the first time.... I put the .257 cal upper on the unregulated lower, and here is what it looks like.... The reservoir is 300 cc, and the gun as shown weighs 6 lb. 9 oz.... Using an aluminum reservoir sure makes a HUGE difference to the weight....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Unregulated_zps5wxd9klz.jpg.html)

Well, the first shot is always an exciting and nervous time.... My Great White was at 3400 psi, so that was the fill pressure I used.... I sized some 82.5 gr. bullets, about in the middle of the weight range I hope to use, set up my Chrony and fired the first shot.... VERY loud, and 978 fps (175 FPE).... I increased the SSG gap from the 1 turn I had it set to, a turn at a time, and it made NO difference to the velocity, so I was firmly up on the plateau, and using a lot of air, the pressure in the Great White dropping a bit with each shot.... Suddenly I got a huge BRRAAAPPPPP which dropped the pressure about 100 psi.... I backed the SSG out a couple more turns, and it did the same thing.... after a couple more big burps, it was time to try something different.... I removed the SSG and set the preload on the 13 lb/in. spring to zero, and reinstalled it with 1 turn of gap.... by this time the pressure was down to just over 3000 psi, and I got a nice sharp report, still pretty loud, and 933 fps (160 FPE).... I started increasing the gap on the SSG, and the velocity stayed the same, but the gun was getting progressively quieter, but still using a lot of air.... Suddenly on one shot, all I got was a click.... Hammer hit the valve, but the gun did not fire.... I started cranking the SSG back in to increase the hammer strike, but even with zero gap, no joy.... I figured something inside the valve had failed, so I degassed the gun and pulled it all apart.... This is what I found....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Broken%20Valve_zpsa3kdn2zs.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Broken%20Valve_zpsa3kdn2zs.jpg.html)

The slotted wheel on the front end of the valve had sheared, and the sleeve over the poppet was no longer attached to the valve, but travelling with the poppet.... This meant there was no balancing force left on the poppet, so no wonder it would not open with the very light hammer strike.... If you ever need proof that the ART/SS valve reduces the required hammer strike, there it is.... I have tried to wrap my brain around where the force came from that sheared that wheel, and for the life of me, I can't see how there is any force on it, with the poppet free to slide inside it.... but there obviously is.... I am using a stepped poppet, with a 1/4" small end and a 3/8" big end, inside that sleeve, so the difference in those areas creates a balancing force of 184 lbs. at 3000 psi (258 lbs. at my 4200 psi MSWP).... If that force is "lifting" the poppet away from the seat to reduce the 464 lb. closing force (at 4200 psi) to "only" 206 lbs.... then I guess it must be "pulling" that sleeve downwards (towards the seat) with that same 258 lbs. of force (it has to go somewhere).... That was enough to shear the four very thin webs between the slots in the wheel that was holding it....

The first shots met or exceeded my expectations, but time for a redesign of that wheel....  ::)

Bob

Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 01, 2018, 04:44:08 PM
SUCCESS !!!

I made a new wheel to mount the front of the valve thimble, with eight 5/32" holes (a total area twice the valve throat), and with the center twice as thick and the webs between the hole more than twice as long, and twice as many of them.... I don't think I will have any more problems.... I put the gun back together and filled it, and my Great White is now down to about 2900 psi.... I installed the 6mm upper instead of the .257, using the same transfer port, and it sealed great.... I sized some of the 61.3 gr. Bowman bullets (a Lyman 257420, scaled down to 6 mm) to 0.243", and replaced the hammer spring with the weakest 3" long spring I have, one of 0.055" wire with a rate of 11 lb/in.... I set the preload to zero, the SSG gap to 1 turn, and shot the first 6 mm bullet.... It ripped through the Chrony at 1007 fps (138 FPE)....  8)

The gun was pretty loud, so I increased the SSG gap 2 turns as a time, recording the velocity as I went.... It didn't start to drop significantly until I was 7 turns out, and then it was still 990 fps.... I changed the gap only 1 turn at a time after that, recording the velocity until 14 turns out from zero gap, at which point it did not fire.... Turning it back in just one turn, the gun shot at 800 fps.... So, I had an adjustment range of about 200 fps before the valve fell off the cliff.... I now have a digital pressure gauge, so I put that in between my tank and the gun, so that I could measure the pressure drop per shot to determine the efficiency.... I started at 12 turns of gap (0.428"), filled the gun to the pressure remaining in the tank (2840 psi), closed the valve, let the pressure settle, and then fired one shot, let the pressure stabilze again and recorded the difference in pressure, and the velocity.... I reduced the gap a turn, and repeated the procedure, recording the velocity and pressure drop at each setting until I was back to 1 turn of gap.... Here are the results....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Plateau%202800_zpsicuylijh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Plateau%202800_zpsicuylijh.jpg.html)

I can't believe how easy the digital gauge makes it to accurately measure the pressure drop for just one shot.... The hardest thing is to try and get the reading at the same temperature each time.... The gauge is soooooooo sensitive that after a shot (which cools the reservoir from expansion of the air during the shot), that you can watch the gauge rise slowly as the reservoir returns to room temperature.... The best way is after you close the tank valve, before the shot, wait a minute or so for the temperature to stabilize, record the starting pressure, take the shot, and then after the shot wait until the gauge has stopped going UP and record that as the end pressure.... and then subtract to get the drop.... From there, my spreadsheet calculates the FPE and FPE/CI, with the only two inputs needed the velocity and pressure drop....

The plateau, at 2800 psi (which is what I had left at the end of the testing), is basically 1000 fps, and the useful knee of the tuning curve runs from 7-12 turns of gap.... With this 61.3 gr. bullet, it looks like about 9 turns of gap (about 5/16") is the sweet spot, giving 960 fps (126 FPE) at an efficiency of 1.24 FPE/CI.... The pressure only drops 80 psi per shot on the 300 cc reservoir, so it will be about twice that on the 150 cc plenum of the regulated version.... That is only about a 6% drop, so I should be able to regulate at the 2800 psi I ran these tests at, at least with this bullet, maybe 100 psi less with the 58.3 gr HP version.... More testing will produce similar information for the other bullet weights I have, but first I have to refill my Great White.... I have a 3000 psi regulator I can tether to, it will be interesting to test the 73 gr. bullet at that pressure.... I will need to get a weaker hammer spring in order to reduce the SSG gap to a more reasonable 1/8" or so.... The cocking force the way the gun is tuned now is less than 8 lbs.... MAN, do these ART/SS valve ever work to reduce that, I'm VERY impressed, and happy with my first effort building one.... and only 2 failures along the way....  ::)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on March 02, 2018, 02:47:11 AM
Great work Bob!! Nice efficiency number's too.

Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 02, 2018, 02:16:07 PM
I had a slight leak, and the reservoir was empty this morning, so while I was filling my Great White this morning I pulled the gun apart and replaced all the O-rings.... Afterwards, I found there was still a slight leak through the valve.... Soapy water on a fingertip pressed to the end of the barrel (with the bolt closed) was met with a steady stream of small bubbles.... I don't know if it is the O-rings in the valve, or the poppet not seating perfectly, but after my tank was filled and I tethered it to my 3850 psi output regulator and fired it a few times the leak is almost gone.... I think with time and use, it may seal up OK.... I sized some of the 82.5 gr. bullets to 0.257", set the SSG gap to 1 turn and fired the first shot at this pressure.... 1010 fps for 187 FPE !!!

I followed the same procedure as yesterday with the 6 mm, gradually increasing the SSG gap until the valve quit opening, and recording the velocity at each setting.... Since the regulator was topping up the reservoir after each shot, I was unable to record the pressure drop to figure out the efficiency.... However, I did establish the tuning curve for the .257 when tethered at 3850 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Plateau%203800_zpstzfmhqis.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Plateau%203800_zpstzfmhqis.jpg.html)

As you can see, with less than 5 turns of gap, the gun is operating on the plateau, just above 1000 fps.... The usable part of the knee is from 7-11 turns of SSG gap.... Surprisingly, the sweet spot was at 9 turns of gap, exactly the same as the 6 mm at 2800 psi.... I would have thought that the hammer strike required would have increased a lot with the 1000 psi increase in pressure (certainly in a conventional valve that is the case).... but it didn't, so one more thing I have learned about (my version) of the SS valve.... I then set the gap back to just 1 turn, to put the gun back to maximum power, and tried all the different bullet weights I have in .257 cal.... Here are those results at 3850 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20FPE%20at%203800_zpsnxzgi5re.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20FPE%20at%203800_zpsnxzgi5re.jpg.html)

It was driving the 66 gr. 257420 HPs nearly at Mach 1 (VERY loud), and the 73 gr. 257420 solids at 1060 fps (182 FPE).... Bullets in the most likely weight range for this gun (82-93 gr.) were shooting 970-1010 fps (186-196 FPE), and the heaviest BBT I have, the 113 gr. FN, was able to reach 895 fps (201 FPE), with the 100 gr. BBT hitting 952 fps (201.3 FPE).... Drop about 4% off those velocities to allow for tuning down to where the efficiency is acceptable.... and I have a .257 shooting at 170-180 FPE.... This is about 20 FPE less than my Monocoque, which has a 5" longer barrel, at the same pressure.... My .257 Hayabusa, running the same barrel length but at only 3000 psi, peaked at 160 FPE and was tuned to shoot at 130-135 FPE.... If I want to tune this gun down to use the 257420s (FN or HP) all I need to do is regulate it to a lower pressure.... At the other end, I can drive my heaviest two BBTs fast enough to find out how they work in the 10" twist of this barrel.... so this gun will eventually prove invaluable for bullet testing.... exactly what I wanted.... With a MSWP of 4200 psi, I will be able to shoot the 113 gr. BBTs in the mid 900s....

I did one other test today.... After filling with the regulator to 3850 psi, I disconnected it from the tether and shot 3 shots, allowing the pressure to drop, just to see what happened.... I was back to using the 82.5 gr. bullets, and I had the SSG gap set back to 9 turns.... The velocities ran 952, 953, and 940 fps, averaging 165 FPE.... According to the small gauge on the side of the reservoir, the pressure dropped about 400 psi, which would indicate an efficiency of about 1.0 FPE/CI.... not a very accurate determination.... but shows me I am in the ballpark at that power....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 03, 2018, 04:56:48 PM
I spent the day today working on the forestock and BiPod mount for the unregulated gun.... The stock is a 10" long piece of 1-1/4" ABS plastic pipe.... It fits loosely over the main tube, and at the back fits under a notch in the receiver designed to clamp it in place against the top of the tube.... That leaves a gap at the bottom of just under 1/8".... At the front there is a curved, taperered shim inside the bottom of the tube, made from a piece of aluminum barstock.... It was quite complicated to machine, because the inside fits the 1.25" OD of the reservoir, and the outside fits the 1.36" ID of the plastic pipe.... and of course the two radii are offset.... I started with a short piece of 1.5"D bar stock, drilled a 1.25" hole 0.055" off center, then chucked it in the lathe and turned the outside down to fit inside the plastic pipe.... I ended up cutting over half the circle away, leaving a crescent shaped piece less than 1.25" wide by 1" long.... I took a short piece of Picatinny rail, milled a concave in the bottom to fit over the outside of the plastic pipe, then drilled and countersunk two holes in it for a pair of 6-32 SHCSs.... These went through two holes in the plastic pipe and were tapped into matching holes in the crescent, so the whole thing went together like a sandwich, with the plastic pipe the filling.... I had made the crescent just a bit too tight a fit, so a drum sander relieved it enough so that the complete forestock would slide over the main tube and back to fit into the notch in the front of the receiver.... Two setscrews tapped through the plastic pipe and crescent, one either side of the Picatinny rail, secure it against the reservoir, pulling it down tight against it, just like the receiver does at the rear.... It looks nice, and feel right, and is very solidly mounted.... I then attached the BiPod to the Picatinny rail, and mounted the scope my wife gave me for Christmas.... This is what the finished rifle looks like, complete with the Harmonic Tuner as well....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Completed%20257_zpsbzvp2ae6.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Completed%20257_zpsbzvp2ae6.jpg.html)

The scope is a BSA 4-14 x 44 Side Focus FFP on medium height Hawke mounts.... The gun as shown s 44.5" long, and weighs 9 lbs. 5 oz. and without the BiPod it is 8 lbs. 14 oz.... Without the Tuner, it would be 8 lbs. 6 oz.... and the bare rifle, as I said before, only 6 lbs. 9 oz....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: sixshootertexan on March 03, 2018, 05:31:16 PM
Great job Bob. Can't wait to see some targets.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Monkeydad1969 on March 03, 2018, 09:15:02 PM
Looks good...sorry I'm a little late to this party.

Joe
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 08, 2018, 02:30:58 PM
I got the 18 mm x 1.5 mm regulator from Travis yesterday, and made a "tiny" tank from a piece of 1-1/8 steel roundbar 3" long, drilled 2" deep and tapped to match the regulator threads.... I already have one for 5/8"-18 NF threads, but this is the first time I needed one for a reg. with the larger threads.... I tested it the way it came, and it was set for 1,800 psi, and fitted with a 3K burst disc on the output side.... so I replaced the disc with a 5K because I need to be able to increase the pressure to as much as 3,200 psi, which is the MSWP for the tube on my regulated 6 mm.... From initial testing I wanted to try 2,800 psi, so I pulled the reg. apart and found some very strange looking Bellevilles.... Intead of a simple concave/convex shape, they were stamped with a ridge in them, halfway between the inside and outside edges.... Travis had sent me some standard 0.032" Bellevilles, which I am much more familiar with, so I decided to use those.... A series stack of the 0.032" thick would not allow me to get a high enough setpoint, and I would normally use the 0.047" ones for this pressure, but decided that since I had enough I would try a series/parallel arrangement using nested pairs of the 0.032" Bellevilles.... The data I had said that arrangement would be not quite as stiff as a single 0.047", which meant it should be easier to adjust.... I tried 6 pairs and got an output pressure of just 47 psi  :o so I added another pair, a total or 14 of the 0.032" Bellevilles, arranged like this....

)) (( )) (( )) (( ))

The reg. body is on the left, and the large end of the piston is on the right.... This arrangement gave me about 2400 psi, and I tried a 0.020" shim and that jumped to 3300.... I ended up with 0.012" of shims and got a nice solid, stable 2800 psi, within about +- 10 psi each time I burped it.... and it returned to the setpoint pressure within a few seconds.... Although the base regulator is Chinese, it has a Delrin ball running on the seat, like the Ninja regs. do.... and seems very stable.... I guess I'll find out if it remains that way in the long term, but I have a good feeling about this combination.... I fitted it to my 500 cc 4500 psi CF bottle, measured up the length I needed to clear the trigger group, cut the tube to length, and set it up in my milling attachment in my lathe to drill the mounting holes for the tank block....

When I made the tank block, I put the holes at a 45 deg. angle to vertical/horizontal, so that I could remove it without pulling the barrel.... This made the setup to drill the holes so that the tank lined up with the trigger group a real PITA.... I ended up using a 5/16" steel rod through the valve screw holes, and a long level with a 45 deg. bubble, and checked and double-checked as I twisted the tube in the milling vice.... I positioned the milling attachment vice in the horizontal and vertical to drill the hole in the middle of the tube, and the correct distance from the end, and with much trepidation, drilled the first hole.... I deburred it while still in place, slid in the tank block and threaded in one screw, and the alignment looked good, so I drilled straight through the tube, and now had two holes.... I loosened the vice, turned the tube 90 deg., inserted the steel rod through them, and used a machinists square on the bed of the lathe to set the tube perfectly, and then checked the distance from the end, and drill the other two holes.... After deburring, all four screws went in with my fingers, and here is the result....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Tank%20Block%20Fitted_zpspnsypzz0.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Tank%20Block%20Fitted_zpspnsypzz0.jpg.html)

The next thing I have to do is build another set of "guts" for my version of the ART/SS valve.... Based on the results of the first one, I have more confidence in my ability to make a second one that will hopefully work "fresh off the lathe" compared to the long learning process I had the first time around.... Once the second valve is complete, I will be able to assemble the pressure tube and see if it holds air.... The tank / regulator assembly is currently sitting with 1500 psi in it and seems to be holding perfectly.... The plenum is exactly 11" long inside, which makes the volume including the valve 165 cc....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 10, 2018, 01:36:51 PM
I spent yesterday making the "guts" for my SS valve.... I already had the body done, but this is a fiddly job, requiring accurate turning of the plastic poppet, including the O-ring grooves, spring seat and sealing face, plus drilling for the stem and vent.... and then making the matching thimble that it rides in from steel, and mounting it to the perforated wheel in the front of the valve.... In case you are wondering why I am not showing photographs of these parts, it is out of respect for Travis, who is applying for a patent on the design.... Anyways, I got it assembled last night, and had a slow leak out the exhaust port, which I cured today by taking another skim off the poppet sealing face and re-lapping it to the valve body.... After assembly with the 6mm upper, and a few test shots, it is now sitting for a leak-down test until tomorrow.... I used my "tiny" regulator test tank instead of the 500 cc CF bottle, so that I can drain the gun if it needs work without wasting all that HPA.... Once the gun is fully sorted, then I will simply unscrew the small steel "cylinder" from the regulator and spin the CF tank on in its place.... Here is what it looks like at the moment....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/Regulated%20for%20Testing_zpsozzbopsf.jpg.html)

My digital gauge is on the inlet, just so I can keep check on the pressure.... I will tether the gun to my Great White for testing by connecting to the male Foster on the inlet of the gauge.... The regulator is set for 2800 psi, and this gun has not been tested before, previous testing was done on the 300 cc unregulated gun, whereas the plenum on this gun is just over half the size, at 165 cc including the valve volume.... I backed out the SSG gap until I saw a slight decrease in velocity, I would have gone further, but I don't have enough travel with the 11 lb/in spring, I will have to fit a weaker one.... I like to tune so that the velocity is 3-5% below the plateau to have decent efficiency.... I did find the plateau velocity with the three bullet weights I have, as follows....

61.3 gr. Bowman (257420 copy).... 993 fps (134 FPE)
63.8 gr. NOE 245-64 FN.... 971 fps (134 FPE)
73.4 gr. NOE 245-74 FN.... 913 fps (136 FPE)

I also have HP versions of all three, about 3 gr. lighter, which I did not test.... I am pleased that the velocity is very close to the same (within about 1%) with the smaller plenum, although it is over 1.2 cc per FPE so I did not expect a dramatic power loss.... It should be large enough to work fine on the .257 cal. upper as well, should I wish to shoot it on the regulated lower....

Now to get a weaker hammer spring so that I can tune this beast down a bit....  ::)  8)

Bob


Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Christopher on March 10, 2018, 06:07:56 PM
Nice setup on the testing apparatus. Bet you have to watch it filling that little vial up with HPA!! ;)

Chris
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 10, 2018, 08:14:42 PM
Not really.... it's so small there is no heat buildup.... The HPA passes through the regulator and fills the plenum which is 165 cc.... then once it hits 2800 psi, the tiny tank fills from there to tank pressure very fast....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 16, 2018, 03:02:06 PM
Catch-up post on progress.... These occurred over the last week or so....

I have run into an interesting little hiccup with the regulated gun.... The new valve I made is as identical as I could to the old one.... It functions fine, and reaches the same plateau velocity at the same pressure, minus a few fps for the 165 cc plenum instead of the 300 cc reservoir.... However, it takes MUCH less hammer strike to reach the plateau, and it appears to have very little velocity adjustment range before hitting the cliff.... I am not 100% sure about the latter, because I cannot reduce the hammer strike to the point where the velocity drops much, and then one more turn (but right at the edge of my adjustment) it quits opening....

The only thing I noticed on disassembly is that the shiny mark on the poppet that should indicate where it is sealing is near the throat (5/16") instead of near the outer edge of the poppet (3/8"), where it was on the original valve.... Both surfaces were turned at 90 deg. to the axis of the valve, and have been lapped in.... The big end of the poppet is 3/8", the small end is 1/4".... with a 1/32" bleed hole to the exhaust port and a 1/16" "jet" in the front.... I know that the area of the seal on the poppet can affect how easy it opens, so you think that is what I am seeing.... If so, cutting a thou or two of concavity in the poppet to force the seal to the outside edge should cure that....

I am still trying to wrap my head around why these valve require so little hammer strike.... There must be something going on after the poppet cracks off the seat, driving the valve open.... Since I am running effectively no jet (a 1/16" hole in the front) the only thing I can see causing the valve to "blow open" is the delay that the 1/32" vent through the poppet, from the exhaust port to the inner chamber, causes in the pressure in that chamber rising to HPA pressure.... Once that chamber reaches HPA pressure, the only closing force left is the stem diameter times the pressure, which we expect.... but if the chamber pressure lags the exhaust port pressure, during that lag time there is an opening force on the poppet....

I really have to restrict myself to one change at a time....  ::)

I took the valve apart today and drilled the vent in the poppet out to 0.040" (from 0.032") and undercut the seat on the poppet to move the sealing edge back out to the outside edge, like on the other valve.... Well, the gun is back to requiring the same SSG gap with the lightest bullets as before, instead of less hammer strike when the seal was further in, on the edge of the throat.... and I attribute that to moving the seat out to where it should be.... However, as I increase the bullet weight I seem to have lost velocity, and more hammer strike is required to hit the plateau.... I didn't do a lot of testing, because the valve is leaking slowly out through the barrel, which I think is the seat leaking again.... I'm not 100% sure, but I think the larger vent hole through the poppet, which in theory should not blow open the valve (as quickly) because the pressure inside the balance chamber should be rising quicker.... is doing that with the heavier bullets, but little change with the lightest one....

The more I work on this valve, the more confused I become....  :(

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 16, 2018, 03:33:53 PM
OK, today I actually made some progress instead of going backwards.... I think....  ;D

I pulled the valve out of the regulated gun yet again, and drilled the vent hole in the poppet out to 3/64" (0.047").... This is now 50% larger than I started with, which means the area is 2.25 times as large.... The idea is to get the balance chamber to fill from the exhaust port the instant the poppet cracks off the seat, hopefully before the pellet even starts to move down the barrel.... This should prevent (or at least reduce) the valve's tendency to "blow open" the instant it is cracked, which I am pretty sure is the reason for the "cliff" on this and the Cothran valve.... While the Cothran has virtually no velocity adjustment between the plateau and falling over the cliff, the ART/SS valve has a pretty fair velocity adjustment range where you can reduce the velocity, and improve the efficiency, before the valve stops cycling properly, and the velocity plummets over the cliff....

The first tests with this valve (compared to the first valve I made which is in the unregulated gun) had a narrow adjustment range, and required even less hammer strike than the first valve, in fact so light I could barely back the hammer strike down to find the cliff.... I took it apart and drilled the vent hole out to 0.040" and made a slight concave in the poppet seat to move the seal back out to the outside edge, and got back to where the first valve was, with a bit more hammer strike required (the larger vent), and a similar adjustment range between the plateau and cliff.... but the valve was leaking and had to come apart again.... I drilled the vent out even bigger, to 0.047", and it looks like I fixed the leak.... The result is that it took more hammer strike to get the same velocity, although still wayyyyyyyyyyy less than a conventional valve with a 5/16" throat at 2800 psi would require.... What I also got, just as I had hoped for, was a MUCH larger adjustment range between the velocity and where the valve stopped functioning.... In fact the cliff has basically disappeared....  8) .... I can adjust the velocity down to under 500 fps by just increasing the SSG gap, something I have NEVER seen before with my version of the ART/SS valve....

All is not perfect, however, because as you increase the hammer strike, and the velocity approaches the plateau, I go through a period of severe hammer bounce.... not a machine-gun but a real BUURRPPP.... and then as the SSG gap gets very small the hammer bounce disappears, probably because the valve is open until the bullet leaves the muzzle (gun is really loud and kicks) which is dropping the pressure in the exhaust port and not slamming the valve closed as hard.... I had been running no preload on the spring on the SSG, which isn't great for resisting hammer bounce, so I added 2 lbs. of preload, and then 4 lbs., and the period of hammer bounce got less each time, but of course I had to increase the SSG gap to get off the plateau and back to the adjustable portion of the curve.... Instead of running about 9 turns of gap (with no preload), I am running about 12 turns (with 4 lbs. preload).... However, I am delighted with the wide velocity adjustment range, so I think I'm on the right track, and the gun is still VERY easy to cock....

One of the cures for hammer bounce is a light hammer, of course, and it works well on a gun where you have lots of hammer strike available (without excess cocking force).... In a gun with an SSG, it generally reduces the gap because of the drastic reduction in hammer momentum, which allows more lift and less dwell.... The plan is to make a MUCH lighter hammer, I think I will try one with no metal core at all, just straight MDS.... May as well start there and back up if I have to....  ::)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 17, 2018, 01:15:08 PM
Remember what I said about two steps forward, one step back?.... Well the all MDS hammer I made is too light to deliver maximum power with the valve with the 0.047" vent through the poppet.... Even with putting in a 14 lb/in spring, at 5 lbs. preload and zero gap on the SSG, I can't quite reach the plateau with the 61 gr. bullets, and I'm down about 10% on velocity (20% in FPE) with the 74 gr.... The good thing is that the shot cycle is a nice clean SNAP (although a loud one), with NO sign of hammer bounce.... However, the large vent, which is intended to make the valve more conventional in operation by eliminating (or reducing) the "blow-open" cycle is doing exactly that.... Basically the valve is operating like a conventional valve that is easier to crack, but that's all....

I have no doubt that by making a hammer that is in between the 32 grams I have now and the 59 grams I had before (both with the 11 gram cocking handle installed) I could find, somewhere, the perfect combination.... However, although not uncomfortable by any means, the cocking force is WAY greater with the light hammer, so I think I have gone too far on the (hard to change) vent size.... Before I pull the valve and make more changes, I am going to make an MDS hammer for the unregulated gun, which is working great except for having too large a gap in the SSG (about 5/16").... The valve in that gun has the original 0.032" vent through the poppet, so has a tendency to "blow open" but it looks like a lighter hammer will drastically reduce that tendency, so it may turn out that a light hammer with the small vent is the perfect combination....

It certainly makes sense to try that before deciding how to proceed with another round of changes on the valve in the regulated gun.... especially because changing out the hammer doesn't even require degassing the gun....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 17, 2018, 04:59:18 PM
I made an MDS hammer for the .257 unregulated gun, and it works perfectly.... I was able to run a bit of preload on the 11 lb/in spring and reduce the SSG gap.... and every shot was crisp with no hammer bounce.... and I was able to push the gun right up to 185-190 FPE at 3800 psi, which is more than I would ever run it because it would use too much air at that power.... I backed the power down to 950 fps with the 82.5 gr. bullet (165 FPE) and ended up with 1 lb. of preload and 8 turns of gap on the SSG, which gives me a cocking force of just 9 lbs.... If I go to the 100 gr. bullet I need to reduce the gap a couple of turns, and if I drop back to the 73.4 gr. 257420 I have to increase the gap a couple of turns to keep it under 1000 fps.... Between the easy preload adjustment and gap adjustment, I can tune the gun from a "mild" 130 FPE up to about 180 FPE before it becomes an air hog....

With the gun set for the 82.5 gr. bullets I filled it to 3850 psi (all the pressure that was in my tank), with my digital gauge connected to the gun, shut off the tank and drained the inlet side of the gauge (it has a check valve for that purpose) and shot a 5-shot string as follows....

953
948
947
935
911

The ending pressure was 3350 psi (it used exactly 100 psi per shot from the 300 cc reservoir), and the first 4 shots were within a 2% ES.... I know that at 4000 psi at this setting the velocity is slightly lower, so I will have 5-6 shots within a 2% ES when off tether with a  4K fill.... and of course tons of shot when tethered to the regulator within a few fps of 950.... The 500 psi pressure drop over the 5 shots averaging 939 fps (162 FPE) works out to an excellent 1.28 FPE/CI, which I am more than pleased with at that power with a .257....

The combination of my version of the ART/SS valve and the lightweight MDS hammer is a real winner.... The gun is easy to cock, has tons of power, and when dialed back about 5% below the maximum is also very efficient.... I am sure setting the power lower would get VERY impressive efficiency numbers, but what's the point, this is a long range Varmint gun.... This valve has the original 1/32" vent through the poppet, which I am now confident is a better choice than the 3/64" I tried in the regulated gun.... Something in between, like the 0.040" vent I tried briefly, would increase the hammer strike, but now that I know the original setup works well when used with an MDS hammer I think I will just stay with the 1/32" vent.... I would like to get a couple of 8 lb/in hammer springs and run them with more preload, so that I can reduce the SSG gap a bit more.... but for now this setup will more than do the job....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 18, 2018, 02:04:10 PM
I just tried a couple of Airsoft BBs in the 6mm at 2800 psi.... 1944 & 1963 fps.... So much for the 1650 maximum.... *LOL*.... Next time I have the 6mm upper on the unregulated gun I will try a couple of shots at 3800 psi.... maybe even 4200....  ;)

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Monkeydad1969 on March 18, 2018, 02:16:46 PM
I just tried a couple of Airsoft BBs in the 6mm at 2800 psi.... 1944 & 1963 fps.... So much for the 1650 maximum.... *LOL*.... Next time I have the 6mm upper on the unregulated gun I will try a couple of shots at 3800 psi.... maybe even 4200....  ;)

Bob

Lol.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Alan on March 18, 2018, 03:58:29 PM
Bob, do you remember those old Sierra thin-skinned varmint bullets made for a .22 Hornet or .218 Bee? They used to unglue at about 2,500 FPS, and I suspect the airlift pellets will too. So let us know what happens, and take photos if you can. Thanks.
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 18, 2018, 04:11:37 PM
I didn't have a fresh piece of paper for a target this time.... but when I did the Disco using airsoft at 1750 fps there were nice round holes at 20 ft., one per shot.... but about a 3" group at that distance....  ::)

If I test again, I'll put up a fresh target....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 19, 2018, 03:50:56 PM
I tried to glue up the 0.047" vent through the poppet and redrill it with no success, so today I made a new poppet for my SS Valve.... I am still using the 3/8" big end and 1/4" small end, but I added a thin (1 mm) O-ring inside against the shoulder of the poppet as a bump stop.... It should never touch, but if the valve was driven fully open (or blew fully open) the O-ring bumper would take the shock instead of either the shoulder on the poppet hitting the inside shoulder of the thimble, or the spring going coil-bound.... It was just a safety measure, but also a way to find out if the valve was opening that far.... As I expected, the O-ring made NO difference, which is proof that the valve is not trying to open more than the 0.19" travel before the O-ring hits.... This was a useful piece of information (and expected), and I plan on incorporating this feature into any future SS valves I make to insure they don't break from being overdriven, or from machine-gunning.... I used PEEK for the poppet, not because it was required, but just because I had some and wanted to try it, and it machines nicer than Delrin....

When I reassembled the 6 mm regulated gun I finally nailed it.... I used the 32 gr. MDS hammer, and the 11 lb/in spring with 1 lb. of preload on the SSG guide.... I was able to easily get to the plateau with all three bullets, and have to run 5 turns of SSG gap with the heaviest and 7 turns with the lightest to get about 3% below the plateau, where I want to operate to get reasonable efficiency.... Here is a graph of the velocity vs. SSG gap for all three bullets at 2800 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Plateaus%202800_zpsdgisn6rd.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Plateaus%202800_zpsdgisn6rd.jpg.html)

I am getting nearly 200 fps of adjustment before the valve falls off the cliff, which is plenty, I will never run it that low.... You will note that there is one additional line on the graph, the dotted black line.... I set the SSG gap at 6 turns, and using the 63.8 gr. bullets I tested the velocity adjuster on the back of the receiver that restricts how far the bolt retracts by moving a pin into the J-slot for the handle.... The reason for the slight increase in velocity when the adjuster is turned in 2 turns is that I had to shorten the nose of the bolt 1/16" because it was pushing the bullets too far forward, which made the 73.4 gr too hard to chamber.... This meant that with the bolt handle pulled all the way back in the J-slot it was creating more wasted volume in the chamber, behind the barrel port, which was dropping the velocity slightly.... It shows the importance of minimum wasted volume between the valve seat and the base of the bullet.... From the maximum velocity setting I have 8 turns of adjustment on the 8-32 screw, which moves the bolt nose from the back of the port to nearly obstructing it.... at which setting the velocity is below 500 fps.... The cool thing about this adjuster is that you can easily try different velocities, to find out if there is an optimum for accuracy.... Of course you should adjust the Harmonic Tuner at each velocity, just to make sure what you are seeing is a true velocity effect, not a change of accuracy due to barrel harmonics....

Once I am sure that there are no leaks, I will remove the "tiny tank" and replace it with my 500 cc CF bottle.... At that point I will be able to test the efficiency at various velocity settings.... These two guns are nearing the end of their development, which is a relief because it won't be long before the Motel gets busy and my shop time disappears once more.... BTW, Alan, I shot three more 6mm Airsoft BBs today, all in the mid 1900s, at a new target.... At 20 ft. I was getting about a 1" group, and I was not taking my time and using a red-dot.... The holes in the paper were perfectly round, and there was only 1 per shot, so the BBs are not coming apart....

Bob

Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 20, 2018, 02:25:31 PM
The gun only lost about 100 psi overnight, so I figure that is "good enough" and I installed the 500 cc CF tank today, and attached the AR style stock.... Here is what it looks like....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/6mm%20Regulated_zpsioo1ovzh.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/6mm%20Regulated_zpsioo1ovzh.jpg.html)

As shown it weighs 8.5 lbs., and without the Harmonic Tuner, exactly 8 lbs.... It balances right in the middle of the tank.... I'm very pleased with the way it came out....

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: Monkeydad1969 on March 22, 2018, 08:21:12 AM
Looking good, Bob.

Joe
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 23, 2018, 01:58:48 PM
Well the 6 mm regulated gun has been sitting with the 500 cc bottle on it for a few days, and shows no visible drop in pressure after the initial post-fill cooling.... I topped it up from my SCBA tank, with the digital gauge in between, shut off and bled the tank valve, leaving the digital gauge connected to the gun with a microbore hose (there is a check valve on the "inlet" side of the gauge for this purpose).... I took a couple of shots until I noticed the digits dropping on the gauge, so I knew it was accurately reading the pressure in the 500 cc CF bottle, let it stabilize a couple of minutes, recorded the pressure, and shot 10 shots through the Chrony with the 63.8 gr. bullets, with the SSG gap set at 7 turns.... I recorded the average velocity (939 fps), the ES (11 fps) and the SD (2.8 ), and after a couple of minutes for the pressure to stabilize again (it rises slightly after the string as the tank warms back up to room temp) I recorded the pressure again.... The tank dropped 465 psi for the 10 shots (which averaged 124.9 FPE), which means I used 978 std. CI of air to produce 1249 FPE, which works out to 1.28 FPE/CI.... That should give me about 30 shots per fill (with the VanDerWaals correction), and I am very pleased with that....  I can dial the velocity up or down from there, which will lose or gain shots of course.... but I certainly have a good starting point for testing.... It shoots 982 fps with the 58.3 gr. Bowman HPs at this setting.... should be deadly on Varmints....

Bob
Title: 6mm Hits 2097 fps on Air
Post by: rsterne on March 23, 2018, 06:19:38 PM
I swapped the 6 mm upper onto the unregulated gun tonight and filled it to its MSWP of 4200 psi.... I set the SSG to just a whisker of gap and fired one shot to settle things, topped it up and fired two shots with the 73.4 gr. bullets.... 1028 & 1029 fps (173 FPE).... Then I did something I have just been dying to try ever since I came up with the idea of building a 6mm.... I loaded up a 1.8 gr. Airsoft BB, topped it up to 4200 psi and took a bead through the Chrony.... 2093 fps.... repeated it.... 2097 fps.... once more.... 2087 fps.... That gives a three shot average of 2092 fps (17.5 FPE) with a basic PCP, just shooting very light ammo.... No special equipment, just a standard SS style valve, porting that turns through 180 deg., and a rifled 29" barrel that is a poor fit on the BB.... it will actually roll out the muzzle if you hold it pointing downwards.... Running air at room temperature (the pressure in the 300 cc reservoir dropped ~ 250 psi each shot), not Helium.... Lloyd still holds the record at 2162 fps.... but he better be looking over his shoulder....  ;D

Bob
Title: Re: Any Interest in 6mm ? - Build Thread
Post by: rsterne on March 24, 2018, 12:17:38 PM
Although I plan on running the .257 barrel on the unregulated gun, while I had the upper removed to try the 6 mm on it, I thought I would try the .257 upper on the regulated lower.... It had a slight leak in the transfer port area, but I did my testing anyways.... Here are the results for the 73.5 gr. Lyman 257420 at 2800 psi....

(http://i378.photobucket.com/albums/oo221/rsterne/6mm%20Sporter/257%20Plateaus%202800_zpsd0uejkoy.jpg) (http://s378.photobucket.com/user/rsterne/media/6mm%20Sporter/257%20Plateaus%202800_zpsd0uejkoy.jpg.html)

At 5% below the maximum velocity I was at 894 fps (130 FPE) at 8 turns of gap on the SSG, and the efficiency was 1.17 FPE/CI.... While that is similar to what I was getting on my .257 Hayabusa, it was a little below the 1.28 FPE/CI I got on the previous testing, which I attribute to the leak.... I was either losing a bit of velocity (likely), using more air (unlikely), or both.... but no question it would affect the FPE/CI either way.... If I was going to set this gun up as a regulated .257 I would likely bump up the setpoint pressure to 2900-3000 psi, although that may not be necessary with the 66 gr. HP version I have of this bullet, it might well shoot better at this pressure....

This pretty much completes the basic testing of these two guns.... I am extremely pleased with the results for both power and efficiency.... The plan is to put the 6 mm upper back on the 2800 psi regulated gun and run the .257 barrel on the unregulated version, and tethered it at 3800, but tune it for a few shots off tether.... All I hope now is that the snow disappears before the Motel gets too busy so that I have a chance to see how they shoot....

Bob