Author Topic: Tale of THREE BRods - .25, .30 and .357 Completed, Page 12 !  (Read 22193 times)

rsterne

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Re: Tale of Two BRods
« Reply #60 on: January 25, 2017, 06:40:15 PM »
Yep, Delrin (acetal) is tougher than Teflon, but harder, so doesn't crush to seal as easily.... It just has to be more precise for length, and PEEK would be even harder, and more accuracy for length required.... As I said, I have never had an issue with the Teflon before, I think this was due to having to thin out the bottom of the TP because of the O-ring that protrudes into the 3/8" hole in the Cothran valve.... I wish the valve had a simple milled recess, all metal, but it doesn't, so I will figure out a work-around.... I think the O-ring, being resilient, allowed the thin TP wall to flex outwards and rupture.... then the HPA escaped to the OD of the TP and collapsed it.... I may make a brass TP, and seal it at the top with a 1 mm CS Metric O-ring....

Bob
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Alan

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Re: Tale of Two BRods
« Reply #61 on: January 26, 2017, 06:17:05 AM »
Self-reenforcing acetal (Delrin) is available in about a dozen different mixes (http://what-when-how.com/materialsparts-and-finishes/acetal-plastics). Thus is pays to select Delrin carefully, and not just by its trade name.
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Alan

I have an Omega compressor. If you're a fellow Guild member, and you pass through Roswell, NM, I'll fill your portable tank as a courtesy.

caniborrowsomeammo

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Re: Tale of Two BRods
« Reply #62 on: January 26, 2017, 06:55:31 AM »
I don't use the O ring as a seal. I cut to over-length then hit ends with mill bit to create a slight curvature to barrel and valve, hand fitting to about a 32nd over-length and compression fitting with the breech to P tube SHCS (to avoid stressing those tiny 4-40's I clamp breech to P tube before torquing them to 10 inch pounds). It seems to give just enough to seal yet not deform port..

As for composition of mix, I don't know :o. I just order mine from Enco (now MSC) and have never seen or noticed a spec of material. ;D
Buncha BB guns that I don't get to shoot as much as I like. Grinding out a living on the farm.

oldpro

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Re: Tale of Two BRods
« Reply #63 on: January 26, 2017, 09:45:41 AM »
 I bored down threw that oring gland and got rid of it and now use a compression oring on both sides of the Tport like on the flex as I had nothing but problems with that sealing method but now its golden.

rsterne

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Re: Tale of Two BRods
« Reply #64 on: January 26, 2017, 12:39:55 PM »
Mine seems to be holding just fine with the brass port, no leaks.... I ran all the tests again, with more bullet weights, and determined the position of the cliff.... As expected, it is a bit different with pellets than with bullets.... The lighter pellets need 1/2 turn less SSG Gap (ie slightly more hammer energy) to stay above the cliff.... Here are those results....



It only takes 1 flat (1/6 turn) on the SSG to go from operating properly to being intermittent, and another flat to see the velocity in the basement.... For the velocity tests with the different bullets I adjusted the SSG so that it was solidly on the plateau.... I added the 62 gr. NOE HollowPoints to the testing today, and also I had some .308 cal 80 gr. BBTs from Accurate that I sized down in 2 step) so that I could try them in this barrel.... All the bullets shot today were sized to 0.300".... Here is the expanded table of results at 1900 and 2900 psi with all bullet weights tested....



Note that the Cothran valve pushes bullets faster at 2900 psi than pellets at 1900.... I didn't do any efficiency testing yet, I'm going to test my modded valve first, putting it through the same tests as I did today with the Cothran....

Bob
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Dairyboy

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Re: Tale of Two BRods
« Reply #65 on: January 26, 2017, 02:02:02 PM »
Coming together nicely  8)
  • Outlook, WA
John 3:16

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rsterne

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Re: Tale of Two BRods
« Reply #66 on: January 26, 2017, 04:27:19 PM »
I started testing my valve today, and got some data at 1900 psi, but when I changed to 2900 the valve started to leak air out the barrel.... I took a bit more data, figuring it would probably be OK, but the leak got worse so I had to degas the gun and pull it apart.... I lapped the seat and poppet and reassembled, and it still leaked.... I put some soapy water in the exhaust port, and it looked like it was bubbling from the right side, where I had plugged the velocity adjuster hole with epoxy when I inserted the larger, longer seat into the valve when I modded it.... I stripped it apart again, cleaned it thoroughly, and put on some penetrating Loctite, the thin green kind that wicks into threads, hoping it would wick into the cracks and seal them.... I will try it out tomorrow, if it still leaks, I may need to make another valve....

I made an interesting discovery down at my bullet trap this afternoon.... It has several sacrificial layers of particle board, backed by a steel plate, and with all the shooting, it had carved a hole through the layers of wood, down to the steel.... I found these two flattened BBT's laying on the floor, just in front of the trap....



Pretty KEWL, what 150 FPE can do.... *grin*....

Bob
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Re: Tale of Two BRods
« Reply #67 on: January 26, 2017, 05:30:48 PM »
Sorta weird that in winter we get SNOW flakes .... Your getting LEAD flakes  :o
  • Old Hangtown ... California
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rsterne

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Re: Tale of Two BRods
« Reply #68 on: January 26, 2017, 08:26:24 PM »
Yep, no two the same !!!

Bob
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Re: Tale of Two BRods
« Reply #69 on: January 26, 2017, 08:36:18 PM »
Yep, no two the same !!!

Bob

Great comeback & so true  ;D ;D
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rsterne

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Re: Tale of Two BRods
« Reply #70 on: January 27, 2017, 09:09:31 PM »
The leak around the insert I made persisted.... so it was time to remake my valve.... I talked to Travis at W.A.R. and he suggested I bore the valve out 1/2" straight through and make a new insert and seal it with O-rings.... Here is what I came up with....



This is a pretty radical repair job, but it gave me the opportunity to do some neat things.... I made the insert a bit longer, to make room for the front O-ring ahead of the port, and enlarged the exhaust port to 1/4" at a 20* angle (same as the 7/32" port was before).... I drilled the throat out to 9/32" to handle the flow of the larger port, and made a PEEK poppet to handle the loads of the larger seat.... This makes the exhaust port basically the same size as the Cothran valve, and as the transfer and barrel ports....

The details of this mod are pretty much explained in the photo above.... The insert is 1/2" OD, sealed with two # 012, 90D O-rings.... There is another hole in the valve for a 10-32 setscrew, in the same plane as the three valve mounting screws, and a dimple in the top of the insert for that to tighten into.... That holds the insert securely in the valve while you machine the port and the three holes for the valve mounting screws.... They are blind holes in the insert, tapped 1/8" deep, using the threads in the valve as a guide, which requires slightly longer valve screws, as the same screws hold the valve and insert in place against the 3000 psi reservoir pressure.... The poppet is made from PEEK, with the stem from 1/8" drill rod, threaded 5-40 into the PEEK.... The stem is 0.070" longer than stock (for my shortened valve).... in a stock length valve it would be even longer....

I assembled the valve and installed it into the tube and it held pressure beautifully.... I then set about testing the .30 cal setup with this new valve.... I had hoped that the PEEK would make up for the larger throat, and not require more hammer strike, but alas that was not the case.... I had to use significant preload at 2900 psi, and a bit of preload at 1900 with bullets.... At 1900 psi with pellets, I had to use preload to max. out the velocity, but the knee of the curve is right about at zero gap on the SSG.... Here is how the gun responds the hammer preload, using the same pressures and pellets as I did for the Cothran valve above.... 6.8 turns out from max. is "zero" gap for the SSG, so at 7 turns and out the SSG is operating, at less than 7 turns there is preload on the valve stem....



When the hammer strike was on the plateau, here are the velocities I achieved with the various pellets and bullets at 1900 and 2900 psi....



Comparing these maximum numbers to the Cothran valve, at 1900 psi there is virtually no difference in fps or FPE.... At 2900 psi, with pellets my valve is almost there with the Cothran, but with bullets I am losing just a bit with the 62-71 gr. bullets and about 10% less FPE with the 80 gr.... I think I may be running out of hammer strike with the heavier bullets, and the difference between the two valves is now insignificant (as you would expect, with equal ports) except for one thing.... My valve is a LOT harder to open, compared to the Cothran.... I'm using a steel hammer that weighs 104 grams, and a lot of preload on the spring, compared to the Cothran, where I'm using an MDS hammer that weighs 51 grams, and lots of gap in the SSG, in fact I could reduce the preload, or fit a lighter spring.... Don's Powerhouse valve sure is EASY to open.... On the other hand, I can tune my valve down onto the knee of the curve, which should make it more efficient.... I think it's time to start trying to work on improving the efficiency of the Cothran valve by making an adjustable lift arrangement so that I can lower the velocity when using the Cothran valve without lowering the pressure....

Bob

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rsterne

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Re: Tale of Two BRods
« Reply #71 on: January 28, 2017, 03:50:03 PM »
I went back to the tube with the Cothran valve today, looking to experiment with varying the lift at 1900 psi.... First I had to make a hammer with an adjustable striker position.... This is the second MDS Nylon hammer I have made, and this time I decided to make it even lighter, with an aluminum core.... They are pretty simple to make, actually.... I started with a piece of 3/4" aluminum, faced it off and drilled it through with a #3 drill (the tap size for 1/4"-28 threads) and then used a 1/2" end mill to create the spring cavity 3/4" deep.... I then knurled the outside longer than the hammer, but leaving a smooth area I could hold in the lathe chuck.... I bored a piece of MDS to a few thou over 3/4", but about 0.010" smaller than the OD of the knurling, faced both ends square to a length of 1.25", and pressed them together to form this....



I then turned the OD to finished diameter to slide smoothly in the tube, and holding the stub of aluminum in a collet I drilled and tapped two 8-32 holes, one for the cocking pin and one for a "brake" to prevent the adjusting screw from adjusting itself.... I then faced off the length at the nose, added the taper for the sear, and tapped the nose through to 1/4"-28, ground the cup point off a 1/2" long setscrew, and installed it with the allen key hole on the inside.... I then dropped a 1/8" long piece of 1/8" diam. Delrin in the front hole, against the side of the adjuster, and topped that off with a 1/4" long 8-32 setscrew, tightened against the Delrin, pressing it into the threads of the adjuster.... Now I can adjust the striker from flush 3 turns in either direction, which is greater than the length of the valve stem on the Cothran valve, so I can go from full lift to no lift in (just under) 6 turns.... Here is the finished hammer, which weighs 28.4 grams (exactly 1 oz.)....



I had a small scrap of energy absorbing polymer sheet about 3/32" thick from Lloyd, which he used in his Cothran valve experimenting, and cut a washer from it with a 3/8" hole (for the striker to clear) and the OD a snug fit in the tube, and installed it hard up against the back of the Powerhouse valve as a bumper to stop the hammer and absorb it's energy.... I removed the spring guide from my SSG, so that I could access the lift adjuster from the back with a long 1/8" allen key, and using the same hammer spring as before, reassembled the gun.... I set the preload on the spring to zero (with the striker just touching the valve stem) with the striker set flush with the face of the hammer.... Assuming the hammer hits the bumper, the valve stem will be driven open about 0.108", and at 0.036" travel per turn of the adjuster, that means that 3 turns out (proud of the hammer face), the striker will push the valve fully open, and backed out about 2.5 turns below flush, it won't open the valve at all.... That was the theory, anyways....

I reassembled everything, tethered the gun at 1900 psi, loaded up a mag. with 45 gr. JSBs, and took a shot.... I had no idea if the valve would cycle properly at these settings or not, and smiled as the shot went through the Chrony at 978 fps, exactly the same as the plateau velocity I had before.... I checked the velocity with more spring preload and it stayed the same, as expected, then reduced the preload, no change at 1 turn of gap, a few fps less at 2 turns, but at 3 turns of gap it dropped to 284 fps.... OK, so there is the normal "Cliff" for the Cothran valve.... I set the preload at 1 turn negative (ie 1 turn of gap), and started adjusting the lift by moving the striker in and out.... When I increased the lift (striker extended), the velocity stayed the same, as expected.... Then I started backing it out, below flush, to reduce the lift on the valve, while leaving the valve cycling properly by virtue of having lots of hammer strike.... I was hoping to be able to have much finer control over the velocity, to give me the ability to control the velocity on the Powerhouse valve without having to change the pressure.... Unfortunately, I was disappointed....

As I recessed the striker into the valve, at 1 turn below flush the velocity held steady at 978 fps.... I figured, "OK, this valve doesn't need much lift".... At 2 turns below flush, I got 321 fps.... much like I did when changing the preload a turn, the valve either cycled or it didn't.... At 2.5 turns out, or further, the valve didn't open, exactly as I had hoped, no shot at all occurred.... I tried various combinations with more preload on the spring, to make sure that I had LOTS of hammer strike, and could not get away from that annoying cliff.... If I was just 1/6 turn (one flat on the allen key) more recessed than where the velocity was steady at 978 fps, the velocity was unstable, it could  be anything from under 600 to over 800 fps.... As I recessed it more, the velocity range dropped, but it was still not stable, fluctuating 100 fps or more, shot to shot.... If anything, I think the velocity was more stable with the valve lift greater, and reducing the preload.... I'm pretty frustrated at this point.... Travis suggested I try a heavier valve spring, but I don't have anything suitable, unfortunately.... At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....

Bob

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Re: Tale of Two BRods
« Reply #72 on: January 28, 2017, 10:54:32 PM »
 ???
Quote
At this point, I still have no way to reduce the velocity when using a Cothran valve, other than by dropping the pressure....

Sizing down transfer passage on a valve operating in the sweet spot above the cliff I'll assume shifts the cliff just scrambling the sweet spot ???
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rsterne

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Re: Tale of Two BRods
« Reply #73 on: January 29, 2017, 09:01:24 AM »
It reduces the velocity, without really changing the preload required to find the edge of the cliff.... Since the air is still trying to release the same amount of air, the efficiency doesn't really improve either.... I don't think it softens the edge of the cliff any....

Bob
  • Coalmont, BC

rsterne

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Re: Tale of Two BRods
« Reply #74 on: January 29, 2017, 06:22:14 PM »
I took a break from tuning today to work on the Tactical version.... I measured up the length, selected a hole in the adjustment range of the AR style stock that would give me about 14.5" LOP, and then made the new end plug / stock adapter....



As always, I am astounded how long it takes to make a simple part from scratch, designing on the fly.... about 5 hours for this, believe it or not....  ::)

Bob

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