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