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....
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....
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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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. ?
