The owners manual says not to shoot 5.56 military shells regular 223 only. Also twist is best for 55grn or less bullets. I just got my 223 rifle sunday. Will shoot black hills 55gr hornady sx well under ! inch. I only put an old weaver 4.5 power V sires scope on it for bang around coyote gun. Groups smaller that the cross hairs at 100yds. Mine will shoot better if you put your front hand on the sand bag and hold the forarm. Trigger is alittle stiff but no creep. I shot one wolf steel case my buddy gave me , no go stuck in chamber. The 55grn or bigger are better killer on coyote. My main coyote gun is a 22swift but to exspensive too get abused.