How does that .223 barrel fit on that SB-1 frame?
If not so good, then your question is moot. But if it fits "good," I'd have no problem putting a .223 barrel on that SB-1 frame! Would be surprising (to me) if the .223 could stretch that frame considering the recoil a magnum 12gagg gives! If the .223 eventually stretch the SB-1 frame, wouldn't it be gradual enough to see it? feel it?