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Heartland Patriot wrote:Well, since the can of worms has been opened, its actually about the LENGTH of the projectile, not its weight specifically. It just so happens that as you make a bullet longer, it tends to be heavier. The tighter the twist, the longer a bullet that can be stabilized (and thus, generally, the heavier a bullet, too). There is an actual formula for it, but I'm not a ballistics guy or a math wiz. You can do a search online and find it pretty easy, though.

If you want to get real nit-picky, it is NOT about the overall length, but the "bearing" length, that is, the length of the bullet that actually engages the rifling. So since the bearing lengths are different, a .308 220 FMJ will not stabilize out of a 10 twist barrel, while a .308 220 30-30 (round nose) bullet will. Essentially everyone who shoots .223 competitively uses Sierra Matchking 69, 77 and 80 grain bullets.

1/9 twist will allow you to shoot bullets up to 69 grains accurately. Get a 1/7 if you are planning to shoot 77s or 80s. 77s and 80s are generally only used for target shooting, most plinkers shoot 55 and 62 grain military type ammo. I used to shoot competitively and used 69s for up to 300 yards, and 80 grain bullets for 600 yards. If you try to shoot bullets too heavy for your barrel twist, they will not stabilize and fly sideways, causing a "keyhole" and crummy accuracy.