Is it possible to have a suppressor that fits a heavy barrel 308 and a 1/2 threaded 223? And if so, how would that work out? Would the heavy barrel be threaded to 1/2" threads?
Yes, but you'll need one with some QD mount that will give you a common thread on each gun. Most manufacturers make their mounts with this in mind so internally they will be 1/2-28 and 5/8-24 to fit .223 and .308 rifles.