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rsterne · Moderator

I measured a few more Ballistics Coefficients for "long range" pellets today (ie round nose & some hollow points).... The gun used was my Uber-Pumper at 20 pumps.... Here are the results....

These measurements were done with a more powerful gun than the previous ones, and there are some trends that are interesting....

The JSB Express at 918 fps had a lower BC than at 844 fps (0.025)....
The JSB Exact at 888 fps was essentially the same BC as at 791 fps....
The JSB Exact Heavy at 835 fps had a higher BC than at 737 fps (0.027)....
These results are consistent with what I observed with the JSB Exacts in .22 cal.... The BC peaks in the 800-900 fps range and then falls off, with the lighter pellets peaking earlier (at a lower velocity).... Of particular note is that the 7.8 gr. JSB Express was moving slower at 25 yards than the 8.4 gr. JSB Exact, despite it starting out with a 30 fps advantage.... The 10.3 gr. Heavy was only 20 fps slower at 20 yards than the 7.8 gr. Express....

There is a clear advantage in muzzle energy for pellets above 10 gr.... Thiis pumper acts just like a PCP in that regard.... At 25 yards, the pellets with the highest residual energy came from that group, and those with the highest BCs were the only ones with over 13 FPE remaining at 25 yards.... I should mention that the H&N Rabbit Magnum, while having a spectacular BC, shot like garbage in this gun, it took me 10 shots just to get three through the Chrony without getting error messages.... Too bad, because they sure hit hard at nearly 15 FPE....

For long range use in this gun there are really only two choices, the 10.3 gr. JSB Heavy and the 13.4 gr. JSB Monster, but the Heavy shot consistently tighter groups, so it gets the nod....

Bob