My Mr. Hollowpoint pellets came in yesterday, and I got a chance to do some testing with them today.... I ordered 100 each of the 50 gr., 53 gr., and 58 gr. in 0.250", and he also sent 10 of a new 53 gr. "4-ring" which I didn't test yet.... I initially set the gun up with the adjustments maxed out and filled to 3000 psi for each shot.... All testing was done tethered to my SCUBA tank but with the tank valve shut off during the shot.... However, I didn't bleed the fill clamp and hose, so it becomes part of the volume of the air reservoir, making the total about 150 cc instead of 135 cc....

The 50 gr. pellets were right on weight, the 53 gr. weighed in at 54.4 gr., and the 58 gr. were 58.8 gr.... The new 53 gr. 4-ring were 52.0 gr.... I miked them, and all the original ones were a few ten-thousandths under 0.250 ", the new 4-rings were right on.... All have his classic large hollowpoint design.... While I was doing the Chrony testing I shot each weight at it's own target.... Note these groups spanned 1600 - 3000 psi, and over a 200 fps range of velocity, and there were at least 15 shots in each group (more with the 58 gr.), and although the range is only 20 feet (in my garage), I did determine that the 54.4 gr. pellets weren't very good in my barrel.... out of every 3 shots, only two were usually touching.... The 50 gr. and 58 gr. put all the pellets into decent groups, and 3 consecutive shots were always one small ragged hole.... The small squares on the targets are 0.10".... Proper accuracy testing will have to wait until our two feet of snow is gone in the spring....



Now for the nuts and bolts.... I tested all three pellets at 3000 psi, 2400, 2000, and 1600 psi, 3 shots with each weight, and recorded the average velocity.... In each case, the gun was set up for the maximum velocity with the 58 gr. at each pressure (hence why I used more of them).... That will mean that the hammer strike was strong enough to max. the velocity with the lighter pellets as well.... Here are the results for heaviest, 58.8 gr. Hollowpoints, plotted on the same graph I used for the 25.4 gr JSB Kings and the 42.4 gr. EunJins....



You can see that at 3000 psi with the 58.8 gr pellets, I got 962 fps, which is 121 FPE, 839 fps (105 FPE) at 2400 psi, 839 fps (92 FPE) at 2000, and 760 fps (75 FPE) at 1600 psi.... The 50 gr. pellets shot 814 fps at 1600 psi and 1002 fps at 3000 psi.... The 54.4 gr. went 788 and 980 fps respectively, and they were still over 100 FPE at 2400 psi.... Heavy pellets sure do up the FPE levels.... I then did some testing using 2400 psi with the 54.4 gr. pellets, and varied the hammer spring preload to see how the velocity and efficiency responded.... Here are those results....



You can see the typical velocity plateau, after which adding more hammer strike gains no further velocity.... I then set the gun up for a shot string starting at 2200 psi, and then another starting at 3000 psi, although by this time I could only get a fill to 2960.... In both cases I got 6 shots with a 5% ES, although without the extra volume of the hose, 5 shots within a 4% ES would be the ultimate outcome....



At 2960 psi, the average velocity was 891 fps (96 FPE) ending at 1860, for an efficiency of 0.83 FPE/CI.... At 2200 psi, the average was 801 fps (79 FPE) ending at 1420 psi, which works out to 0.96 FPE/CI.... Using a pressure in between to achieve a power level in the mid-80 FPE range would probably get the that to over 1.0 FPE/CI....

So for now, this project has reached it's conclusion.... I managed to get 121 FPE at 3000 psi and 105 FPE at 2400 with the 58.8 gr. pellets, and I'm pretty pleased with that.... What started out giving 11 shots at 45 FPE starting at 2100 psi is now doing 6 shots at ~80 FPE from 2200.... which is a huge increase in power at exactly the same efficiency.... I'm sure there is more efficiency to be found in there, but I'd really like to try some heavier bullets, and they would be too long to stabilize in the LW barrel.... Therefore, I think I'm going to order a 28" long .257 cal liner from TJs and start casting my own bullets in 65-85 gr. weights, which will work in its 14" twist.... I'll need to bore out the valve and ports some more, and the goal is to exceed 130 FPE with the 65 gr. bullets.... The only thing I haven't decided is whether to use the new barrel on this Disco, or put it on my Hayabusa.... When I make the parts to convert it into a .224 bench rest rifle, optimizing it for the 41.5 gr. bullets, it would be close to ideal for the 65 gr. .257 cal bullets as well.... So many projects, so little time....

Bob