Will this load stabilize in a 1:9 or does it need a 1:7/8?
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Will this load stabilize in a 1:9 or does it need a 1:7/8?
What is the barrel length? The longer the barrel is and the higher the velocity is, the more you can get away with on slow twists.
Just the same, a 7 would be preferred, with 8 being borderline acceptable in my opinion.
It shoots ok in a 1/8 twist RRA NM barrel I have... pretty well in fact, 1-1.5 MOA if I do my part.
18in. Barrel seems to shoot fast. My Win 55gr FMJ stays around 3150fps (Spec is 3270 from a 24in) so I'd imagine this load would run around 2600ish.
1/7 would be better for a variety of reasons.
Actually, up to 1/9 is very useful, it just usually comes in substandard quality guns. The 1/7 twist was adopted solely because some wonks thought it would be a great idea to have the capability to shoot M856 tracer in the gun. 1/9 will stabilize the M855 load, but not its companion tracer round, so along came the 1/7. BTW, it was never intended for M855 (Green Tip) to be a standard service round for the M16/M4, but only in the M249 SAW. Since we've trended much heavier in projectiles for the caliber, I guess it turned out ok.
Faster twists have some significant external and terminal ballistic advantages as a result of faster rotational velocity--this is especially important with both shorter barrels and longer ranges. Of course the projectile must be robust enough to handle the increased forces without coming apart in flight...