My build.....AR build anyways.

JoeSBP said
thats the reason we went to the 1:7 in the first place.. Our 62gr green tip (and it's new replacement) is more accurate ran 1:9. However the heavier and slower tracers tumble when pushed out of a 1:9. The 1:7 was adopted for this reason, despite a reduction in accuracy.

Yup. But any bullet that's longer or has a forward biased cg can benefit. Like M855 and the new M855A1. Doesn't mean 1/7 is best for the 62gr stuff, but by the numbers it should work as well as 1/8 while 1/9 could give an issue depending on the actual tolerance of the parts involved. There will be the odd barrel that is closer to 1/9.5 or 1/10 but still stamped 1/9. Or cold weather or an ammo lot that's on the lower side of velocity. In those cases, there may be stabilization issues (but not always). Over-stabilization isn't a big issue until drop rate picks up, and that tends to happen beyond 400 meters. So over spinning a round isn't a big concern unless you're after ever last bit of mechanical accuracy.

One of the reasons the 62gr stuff is more accurate in a 1/9, when it's stable, is that the reduced spin rate makes less of an issue out of the binary nature of the projectile. When the steel core is misaligned to the rest of the projectile, it tends to wander in a circle rather than flying 'true'. The M855A1 put a lot of emphasis on reducing dispersion as a result of the manufacturing tolerances. Last I heard, however, it wasn't a massive improvement, but an incremental one. But that was in the really early days when the IC was still a thing.

This is why I tend to recommend 1/7 because "it just works" for most casual cases. It works for tracer, it works for 855, it works for 193, and it works with 77gr SMK too. If all you'll ever shoot is 55gr then 1/9 is great. But I'm a bad predictor of my own future behavior and newbies tend to want to try it all to see what they like. So I prefer 1/7. YMMV.