.222 rem mag is too close to .223 to be worth doing IMO, I think .222 would be a step down ballistically, so that leaves .17 rem, .204 ruger and .223AI. I want to start reloading someday but currently dont so that pretty well kills the AI.
Im pretty solidly thinking .204 ruger will be the way to go if I keep the same bolt. But I believe Ill get the rest of the good out of the .223 barrel before doing that.
Maybe in the meantime Ill find a used M77 bolt with a larger face diameter and open up some more options.
Will an old M77 bolt work in a Mk II? If so I have an old M77 chambered in 6mm rem that could donate a bolt. That would open up some more options like .257 roberts or 7x57 mauser