First of all Mountainman is correct. I theory the 1:9 will shoot 55 grain to around low 70s OK. The faster the twist the heavier the bullet that will shoot best in it! In the 1:9s they usually most like the mid 60 grain bullets best as far a optimum accuracy. However the theory is not always perfect. Most 1:9s will shoot the 55 grain rounds well. As the guys stated, the 50-53 grain bullets will shoot OK and should be fairly accurate as well.I do not believe it will give max accuracy performance but for the average shooter if not shooting on a bench on the bags one would never know the difference. So yes it will shoot them. For example I have a Rock River Elite CAR A-4 with a 1:9 twist. Shooting Federal P223 E ammunition in 55 grain. It will group around 1/2 to 1 MOA at 100 yards with the 16 inch barrel. Which is good for a tactical type rifle. It likely would shoot the 60s grain bullets a little more accurate ??? but I am satisfied with the performance of the 55s. I had previously posted a thread on barrel twist compared to bullet weight if you want to research it.
Correction from previous Post! The M-16 A-1 Rifle has a 1:12 Twist Rate.
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Last edited by Sniper03; 06-30-2012 at 01:20 AM.