MMcfpd
Member
Both of my 7.62x39mm ARs went to the range this morning, one a 16" Model 1 kit gun with an Aimpoint M4 and the other built with a Model 1 barrel that's been cut down to 14.5", with an Aimpoint T-1. Their barrels are both chrome moly with 1:10 twists.
Both were zeroed at 50 yards, and I decided to try 'em on the 100 yard. The 14.5" is new and I hadn't done that with it, and I don't really remember the last time I tried the 16" on the 100.
This may well be old hat to the more ballistics savvy amongst us, but it was a discovery for me. Firing Sellier & Bellot 123 gr. FMJ out of both guns, the 16" was hitting pretty consistently about 2" high while the 14.5" was pretty much on the bullseye (as much as I am on the 100 - the altitude was right, but I still find accuracy with a 4 MOA red dot at 100 yards to be a bit challenging).
A better explanation from those who know is welcome, but my best guess is that the slightly lower velocity that round gets from the 14.5" barrel allows that 123 grain bullet to drop, compared to one flying out of a 16" barrel, enough to be pretty much flat at 100 yards with its 50 yard ballistic profile.
Anyway, the outcome surprised me a bit. I shot a couple of mags out of each and results were unchanged.
Both were zeroed at 50 yards, and I decided to try 'em on the 100 yard. The 14.5" is new and I hadn't done that with it, and I don't really remember the last time I tried the 16" on the 100.
This may well be old hat to the more ballistics savvy amongst us, but it was a discovery for me. Firing Sellier & Bellot 123 gr. FMJ out of both guns, the 16" was hitting pretty consistently about 2" high while the 14.5" was pretty much on the bullseye (as much as I am on the 100 - the altitude was right, but I still find accuracy with a 4 MOA red dot at 100 yards to be a bit challenging).
A better explanation from those who know is welcome, but my best guess is that the slightly lower velocity that round gets from the 14.5" barrel allows that 123 grain bullet to drop, compared to one flying out of a 16" barrel, enough to be pretty much flat at 100 yards with its 50 yard ballistic profile.
Anyway, the outcome surprised me a bit. I shot a couple of mags out of each and results were unchanged.