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Jimro · April 15, 2012, 01:56 PM

Assuming that the barrel length is the same 20" as on a standard AR service rifle...

1:9 shoots up to 69gr HPBT bullets very well, some can shoot 75gr HPBT well

1:8 shoots 80gr HPBT for single load stages, usually 77gr HPBT for "across the course"

1:7 the "milspec twist" shoots 80gr HPBT well, handles 77gr HPBT no problem, but isn't fast enough for 90gr HPBT

Anything 1:8 or tighter is fine for High Power matches. 1:9 is doable, but I only know one person who has done it (and he shoots High Master scores with 69gr SMKs) but is also a .mil sniper in his day job.

If the barrel length changes, then all bets are off. A lot of competitors like a 1:7.8 twist because it stabilizes the 80 grainers a tad better than the 1:8 twist without introducing "bullet imbalance" on the target like a 1:7 can. For the same bullet a 1:8 twist will introduce almost a tenth of an inch less variation on target due to bullet imbalance.

If you have a different barrel length or cartridge combo in mind, let us know.

Jimro

April 15, 2012, 01:56 PM	#5
Jimro Senior Member Join Date: October 18, 2006 Posts: 7,097	Assuming that the barrel length is the same 20" as on a standard AR service rifle... 1:9 shoots up to 69gr HPBT bullets very well, some can shoot 75gr HPBT well 1:8 shoots 80gr HPBT for single load stages, usually 77gr HPBT for "across the course" 1:7 the "milspec twist" shoots 80gr HPBT well, handles 77gr HPBT no problem, but isn't fast enough for 90gr HPBT Anything 1:8 or tighter is fine for High Power matches. 1:9 is doable, but I only know one person who has done it (and he shoots High Master scores with 69gr SMKs) but is also a .mil sniper in his day job. If the barrel length changes, then all bets are off. A lot of competitors like a 1:7.8 twist because it stabilizes the 80 grainers a tad better than the 1:8 twist without introducing "bullet imbalance" on the target like a 1:7 can. For the same bullet a 1:8 twist will introduce almost a tenth of an inch less variation on target due to bullet imbalance. If you have a different barrel length or cartridge combo in mind, let us know. Jimro __________________ Machine guns are awesome until you have to carry one.