I'm having a hard time reconciling the two images, Kraigwy's comparison of M193 and M855 target impacts and JonnKSa's "223REM rifling vs accuracy by bullet weight" and other graphs of his that indicate that 1:12 should be fine with 62gr bullets. If the groupings of a 62gr bullet is 1" for a 1:12 twist (presumably at 100 yards). That should translate, in my mind, to 3" groupings (or slightly higher) at 300 yards.
It appears to me that the 1:12 under-stabilizes the M855. Do we know if there was there a difference in muzzle velocity between the M855 and the 223 in the tests above?
I'm curious b/c I always thought that I was "stuck" with 55gr bullets in my Vietnam-era AR. If I could use 62gr, that opens up more opportunities for ammo.
edit: credit to John for putting together all of this data in one place. Thanks!
I'm right about the metric system 3/4 of the time.