55 gr. BBT HP

I have a hot .25 cal Disco that is a genuine 100+ FPE gun, so I pulled it off the wall today to try some velocity experiments with different size bullets…. I have some 50.4 gr. FN BBTs (NOE 250-51), and also some 58.3 gr. FN (NOE 250-60), plus the HP versions as well…. I tried them as cast (0.250″ nose / 0.252″ drive band), and they were hard to chamber in my TJ’s .25 ACP barrel…. so I sized some of each down to 0.251″, 0.250″ and 0.249″…. I tethered the gun at 2950 psi (it is modified for 3K plus) and both bullets picked up a lot of velocity between as cast and 0.251″, gained more at 0.250″, and then lost about 10 fps at 0.249″, presumably from a small amount of blowby….

The 58.3 gr. FN were well over 900 fps, so I thought I would tune the gun for the 55.0 gr. HP version of that bullet, sized to 0.250″…. Mean looking little devil….

I maxed out the preload and hit 993 fps (120 FPE), and then backed it off a turn and got 965 fps…. At that setting, off the tether, I got 2 equal shots and then a 3rd at about 940 fps, so I backed the preload out a bit more and ended up with 3 shots off tether of 956, 963 and 945 fps (111 FPE average) within a 2% ES…. Tethered, of course, it shoots 956, within a few fps…. which will give me a good platform to test these HP bullets…. The gun is loud, and not very efficient…. but at 110 FPE it should really lay a smackdown on a Marmot…. 

This is a penetration test of the 55 gr. BBT HP in soap at 110 FPE…. The nose came apart…. penetration of the base was 95 mm (3.75″)….

Bob