Going heavy on the 223 I'd expect possible problems with the twist/bullet. But if it's shooting the same across the board I'd guess something with the gun itself.
Past that hit the shooter side.
Vice or no vice, bench or offhand, and how big of a pattern? Last because when I shoot a lot my 'pattern' definition is a lot tighter than currently when I'm not shooting much at all 
Curiousity, otto range?
And because I like to bash them, I've never gotten core-lokts to shoot better than MSOT, "minute of somewhere over there".
