Home Forums Hunting & Shooting Custom Rifles & Wildcats A.I.'ing the R.A.R.?

I was thinking about either the 16" 5.56 or the Predator 22" .223 Ruger American Rifle. Thinking it'd be cool to have the chamber Improved at some point.
My question is, will it feed in the American Rifle Magazine without extensive modifications to the mag? Would it feed through one of the already modified models to accommodate longer bullets (75 A-Max)?