reddot,
Somewhere in my collection of targets that I have shoot in the past, I have a beautiful group fired from my .223 Contender Super 14". I was using a bullet that weighed 60+ grains (I don't actually remember the weight, but I know it was in the 60's...Any bullet I shoot in it in the 40's or 50's shoot well to very well) Anyhow, I have a perfect 3-shot group at 50 yards that measures 'bout 1.5" center to center. That is, center to center of the keyholed bullets!!! All keyholed picture-perfect and the target is classic!
My .223 is a 1-14 twist. I have seen some listed as 1-12. The 1-14 won't stabilize 60+ grainers--The 1-12 might stablize light 60's at a hefty velocity. Still the effort probably wouldn't be worth it. Stay with the 50 to 55 grainers and you will get much better results. Good-luck...BCB