Hatsan .25 cal AT-44S Long with Heavy Pellets
I recently got some 36 gr. Daystate Rangemaster pellets, so I decided to see how they would work in a couple of my guns.... My Hatsan was capable of significantly more power than the way I had it tuned with JSB Kings, so I pulled off the air cylinder, reinstalled the 0.090" stem in the enlarged valve, and tried them out.... It took a few more turns of preload for the gun to be happy with the much heavier pellets, and I tested them against 35 gr. EunJin Domes, plus the (now drastically overpowered) Kings.... Here are the results with the heavy pellets....
http://i378.photobucket.com/albums/o...psc21ef235.jpg
With 8 turns of preload, 2800 psi (193 bar) is the optimum fill pressure, and I got 14 shots within a 4% ES, averaging 68 FPE.... At 9 turns of preload, the first shot with the EunJins was 3% below the peak and I got 12 shots finishing well within a 4% ES, averaging 71.3 FPE.... With the 36.1 gr. Daystate pellets, the first shot was 2.3% below the peak and the 4% ES string was again 12 shots, averaging 72.4 FPE.... By dropping the fill pressure to 195 bar, I can shoot 9 shots (1 full clip) within a 17 fps ES (1.8%), ending at 155 bar.... That works out to a 73 FPE average, and an efficiency of 1.18 FPE/CI.... pretty astounding for that much power.... While 9 shots isn't a lot, I have a 90 CI 4500 psi tank with a 2800 psi regulated output to carry in the field.... By my calculations, that will give me 18 fills, so I end up with a gun that shots at 73 FPE and stays within a 2% ES, one clip at a time....
In terms of accuracy, my initial tests showed that at 32 yards the Daystate pellets would hold groups that could be covered with a quarter.... That's not quite as good as the Kings when kept at about 970 fps, but at that velocity they are only 53 FPE, 27% less power.... I tried the Kings at this setting, and they screamed across the Chrony at 1070 fps (nearly 65 FPE) but their groups were no better than the Daystates.... and both pellets were tighter than the EunJins.... I still have to tune the air stripper to optimize the group size for the Daystates....
While I was testing, I wanted to check the Ballistics Coefficients at this power setting, so I set up the Chrony at 32 yards, and I got the following results....
http://i378.photobucket.com/albums/o...ps00b4bc8a.jpg
In all cases, I used 5 shots centered at the top of the velocity curve, to get the most power and the least variation in velocities.... It is interesting to note the when you push the JSB Kings this fast, their normally great BC is starting to deteriorate, even when measured over 32 yards.... If you checked it over the first 10 yards, I think it would be under 0.015.... They are losing a LOT of velocity and energy in the first few yards when you push them this fast.... On the other hand, the 36.1 gr. Daystate Rangemasters have a great BC, and are retaining over 80% of the muzzle energy at 32 yards.... At 100 yards, they would still have over 35 FPE remaining.... The SR12 Reticle on my Hawke 6-18 x 44 scope will be useful to 112 yards (over 100m) at full power with the gun sighted for a 1/2" kill zone (40 yard zero) with the Daystates.... Here is a photo of the finished rifle....
http://i378.photobucket.com/albums/o...ps55fc1ace.jpg
I'm extremely happy with the results.... I ended up with a a real quarterbore powerhouse at 73 FPE....
Bob
