The 75 grain Hornady AMax loaded to 2.45 oal may or may not stabilize in your barrel. It makes it to 1000 in my 1 in 8 twist 22 inch flattop upper with 24.7 grains of RL15, Rem 7.5 primers and LC brass. This is pretty much near a max load as it exits the muzzle at over 3000 feet/sec. The Hornady 68 grain loaded with 25 grains of Varget or RL15 should easily see you to 600. Once again, this is close to a max load. It works fine in my DCM uppers, but it popped primers in a standard Bushmaster 5.56 barrel.