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PostPosted: Sun Feb 23, 2014 9:50 am 
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Is the hammer spring short enough to get that flying hammer effect?


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PostPosted: Sun Feb 23, 2014 11:32 am 
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Not even close, but with the efficiency I'm getting it's not an issue....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
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PostPosted: Sun Feb 23, 2014 6:44 pm 
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I thought maybe a lighter valve spring would make a difference to the usable pressure range, so I fitted one made from a 2240 hammer spring that was less than 1.2" long, so it had very little preload.... Basically, other than requiring about a turn less hammer spring preload, the gun shot exactly the same.... About the only thing I had left to try was a bstaley O-ring buffer.... Although intended for use with an adjustable length striker, I took a chance and dropped in three #113 - 70 D O-rings and because of the 0.050" I had machined off the steel backer block for the valve they were too short, so I added a "backer ring" under them against the steel block which was 0.050" thick to make up for what I had machined off.... I figured the chances of this being the correct thickness O-ring stack to work properly was slim to none, but at this point I was getting desperate.... I still had the gun set up as per the previous string with the 0.104" barrel port, and to my surprise I got a nice flat 17 shot string from 650-680 fps (about 18 FPE).... I tried one more turn hammer spring preload and the velocity moved up to 700, but right at the beginning of the string and then a dozen shots before it dropped 4%, so I was getting very close.... At this point I had two choices, either take a bit off the O-rings to increase the valve lift, or try going larger on the barrel port.... I decided to simply remove the barrel port restrictor, and boy was THAT the right decision.... I was rewarded with an 18 shot string starting at 698 fps, peaking at 718, and ending at 692.... a 20 FPE average, just what I wanted.... Here are the results....

Image

This was a perfect scenario for the bstaley O-ring mod.... a gun that was overpowered with big ports and tons of flow, tuned down to use tiny sips of air very efficiently.... The total pressure drop was 475 psi, for a staggering efficiency of 1.57 FPE/CI.... I'm still limited to using about 500 psi for a 4% ES string, but with the number of shots, that is no longer an issue.... I can now set the gun up as a repeater using the 8-shot PRod magazine and get 2 full magazines at the 20 FPE level I wanted.... The best 20 shots are within just 20 fps from 1500 psi down to 1050....

So far I had not mounted a scope, so I really had no idea how accurate this gun was.... I borrowed a scope from another rifle, and was rewarded with it putting the 18.1 gr. JSB Heavies into a single 1/4" hole at my 20' inside range.... When a gun shoots like that, I know it's a keeper, and I don't even have to go looking for other pellets, because I know how great these work on Grouse at this power level.... One other thing I'd like to show you is the fill system I have.... I bought the parts from China on eBay for just $16.00, it will allow me to fill the gun from any paintball tank with a 1500 psi regulated output.... It consists of a fill station valve with 3000 psi gauge, an 8" braided hose, and a slide check which came c/w a female Foster fitting.... I bought the three parts separately and the vendor combined the shipping for $9.00.... and I received it in just a week....

Image

Using a 48 CI 3000 psi tank will give me about 20 fills, and even a tiny 13 CI tank will fill it 6 times in the field.... wayyyyyyyyy more than you need for a days hunting.... Tethered to the big tank, I would have about 360 shots available, and over 100 from a 13 CI....

For those of you who might want to try the bstaley O-ring buffer in your FD-PCP, it's as simple as just pulling out the striker and dropping them in against the back of the steel valve backer block.... Use three #113 Buna O-rings of 70 Durometer, and see what you get.... It's too bad the gun doesn't have an adjustable nose on the striker, that would make tuning it a breeze.... but the basic idea is that if you need more power you need to thin up the O-ring stack a whisker (sand the front one down).... and if you need to slow it up more, add a thin shim between the front one and the steel block.... What you are doing is limiting the amount that the striker can open the valve.... which reduces the power and lengthens the shot string.... It works best when you are reducing the power a fair amount as in this case (going from 30 FPE down to 20) where I doubled the shot count.... If the stack is thinner, at some point it does nothing and you get full power.... At the other end of the scale, if you make the stack too thick, the striker won't hit the valve at all, and the gun won't fire.... The distance between those two extremes isn't a lot, probably less than the thickness of a single O-ring....

Oh!, I almost forgot.... While tuning the gun today I was adjusting the preload with the velocity adjuster, and suddenly the gun wouldn't cock.... I couldn't pull the bolt back far enough for the striker to catch the sear.... If I turned the preload a half turn in either direction it was fine, so I suspected that the shoulder on the adjusting screw was off-center just enough to catch on the back of the hole in the striker.... I pulled the velocity adjuster mount off the back of the gun, and sure enough, there was a shiny mark on the shoulder where it had been rubbing on the inside of the striker.... This would not be an issue if the adjuster was backed out further, but I needed to fix it, so I chucked the adjusting screw in the lathe and remove 0.010" (on the radius) so that it was the same OD as the spring and could no longer rub on the inside of the striker.... I reassembled the gun, and not only did it cure the problem and the gun now cocked fine no matter what the rotation of the velocity adjust screw.... but the trigger pull was MUCH improved.... I guess the striker, most of the time, was being pushed offcenter by the shoulder on the screw which caused it to bind on the sear.... So, I killed two birds with the one rock.... I was wondering why the trigger on this gun was so rough, and that was the reason, it was fighting against a binding striker....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Sun Feb 23, 2014 7:22 pm 
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Splendid work Bob, looks like that is going to turn out to be one of the best value budget guns out there! Thanks for the tip on the ebay parts, from your description I was able to find that fill station valve, and then discovered that the gauges are available separately :)

Jim


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PostPosted: Sun Feb 23, 2014 7:38 pm 
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nice stuff Bob little curious buddy :? I while back we had a small disagreement about a check relief valve on a remote fill line, you said it was not a safe thing to have, not sure if you remember it, but yet here you are with one. ?

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PostPosted: Sun Feb 23, 2014 9:29 pm 
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What can I say.... I checked into it and found out that they work fine and are strong enough but the O-rings may not last if the pressure is too high.... This gun is only running 1500 so I figured I'd give it a try....

I don't even remember the thread, to be honest, I probably just dismissed them as being intended for CO2.... my apologies....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Mon Feb 24, 2014 12:54 am 
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No problem buddy, i was just a little confused that you were once dismissing it as unsafe and now your using it :lol:
and yes your correct the o-ring tend to give out on them but Ive yet to see the actual check valve blow on one. :wink:

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PostPosted: Mon Feb 24, 2014 7:13 am 
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How does the pressure in the hose vent? Any risk of it whipping as you disconnect?


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PostPosted: Mon Feb 24, 2014 9:26 am 
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See the little gold anodised think to the right side of the hose thats the check it slides back and forth, no there is no whipping just a release of air.

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PostPosted: Tue Feb 25, 2014 12:16 am 
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Today I modified the receiver to accept the 8-shot .22 cal PRod magazines.... This was NOT my idea, I borrowed it from stalwart on the GTA who originally used a 10-shot .22 cal MRod magazine.... The basic idea is to machine a notch big enough for the PRod magazine in the receiver.... It looks like this....

Image

You can see the back of the barrel which has been machined to 7/16" OD and protrudes 1/16" into the notch, providing a stub for the magazine to clip onto.... I used a 5/8" end mill and the notch is 1/8" deeper than the bottom of the barrel stub.... I removed a small amount of the front of the existing breech opening, and also faced a bit off the face of the bolt to get enough room for the magazine.... Here are the modified barrel and bolt....

Image

I cut the stock bolt nose off 0.40" from the (new) bolt face, drilled and tapped it 8-32, took a piece of 1/4" drill rod 3/4" long and did the same with it and used a 1/2" long piece of an 8-32 screw as a stud to attach the new front of the bolt to the old stub using loctite.... I then turned the shaft of the bolt down to 7/32", and the probe section down to 3/32" and adjusted the lengths so that the shoulder is flush with the back of the barrel port and the probe pushes the pellet just past the port....

The mods to the barrel were tricky.... I used the old front O-ring groove for the rear O-ring and cut the barrel off about 1/8" behind that, losing about an inch of length.... The 1/2" OD portion of the barrel is a lousy fit in the receiver, so when I moved the shoulder over, I made it a better fit.... The locatons of the O-rings, barrel port (on the bottom so not visible in the photo) and the set-screw hole are all critical, as is the 7/16" shoulder.... I didn't add a groove for the third (forward) O-ring I don't see any reason for it.... Also what you can't see, there is an internal O-ring groove inside the barrel in the space between the external O-ring and the back.... That O-ring is a #009 and fits nicely on the 7/32" bolt nose to seal it.... I had to rechamber the barrel of course.... Here is the breech with the magazine in place....

Image

It took a ton of measuring, thinking, drawing sketches, and careful fitting to accomplish this job, and my thanks to stalwart for all his help.... If you want to get your FD-PCP or XS-60C converted as a repeater, please contact him on the GTA Forum....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Feb 25, 2014 7:22 pm 
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Well I got the rifle back together today, and it works beautifully.... I get 20 shots from 1500 down to 1000 psi within 30 fps (4%), 692-720-692, which averages 705 fps (20 FPE) so that works out to 1.66 FPE/CI, which is stellar efficiency at that power level.... The bstaley O-ring buffer really works well to detune this gun for moderate power and lots of shots.... It stuck all 20 shots in the same 3/8" OD hole (at 20') while running the string through the Chrony, so the accuracy will be there I'm sure....

Image

With a Leapers 3-9 x 32AO scope in medium rings the tube easily clears the PRod magazine, although if the turret sticks down very far below the tube on your scope, it may not fit unless, like on mine, it is either in front of or behind the magazine.... The gun as shown above weighs 6 lb. 13 oz., so it's under 6 lbs. without scope, and with the 1" shorter barrel the gun is under 39" long.... I would say that if my son can shoot, the Grouse are in for a really bad time this fall....

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Tue Feb 25, 2014 8:07 pm 
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Nice work Bob.
I think I could manage all you have done with milling the block etc. I would, however, struggle ( with my limited machining skills) to cut the o ring groove inside the barrel.

Could you get away with the o' ring on the bolt ( archer has done his that way)


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PostPosted: Tue Feb 25, 2014 8:58 pm 
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Yes you can, but it will tend to hang up on the magazine a bit and will likely wear out as well.... If you mill the slot 0.060" ahead of the end of the barrel, and then vut off the poading tray and turn the end of the barrel down to 7/16" for the mag to clip onto you may not have to make as many changes.... However, the chamber is very deep on the stock barrel, hence the long pellet probe (it pushes the pellet a long ways past the port).... You may have to shorten the probe to get the magazine out, and for sure you will have to hold the bolt all the back to the back of the slot, against the spring, to change the magazine.... My probe is short enough that once the gun is cocked the probe clears the magazine for removal....

Bob

_________________
Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Wed Mar 05, 2014 10:49 pm 
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I assume everyone figured out that

Quote:
vut off the poading tray

was really

"cut off the loading tray".... :roll:

Bob

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Dominion Marksman Silver Shield - 5890 x 6000 in 1976, and downhill ever since!
Airsonal;
Too many! Springers, Pumpers, CO2, but I love my PCPs and developing them!
Proud Member of the 2000+fps Club!


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PostPosted: Thu Mar 06, 2014 8:23 pm 
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rsterne wrote:
Yes you can, but it will tend to hang up on the magazine a bit and will likely wear out as well.... If you mill the slot 0.060" ahead of the end of the barrel, and then vut off the poading tray and turn the end of the barrel down to 7/16" for the mag to clip onto you may not have to make as many changes.... However, the chamber is very deep on the stock barrel, hence the long pellet probe (it pushes the pellet a long ways past the port).... You may have to shorten the probe to get the magazine out, and for sure you will have to hold the bolt all the back to the back of the slot, against the spring, to change the magazine.... My probe is short enough that once the gun is cocked the probe clears the magazine for removal....

Bob


Your way will undoubtably be the best way and I will try to do it. It all hinges around me machining a groove inside the barrel!! :oops:


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