I picked up a 12 gauge barrel and stock for the SB2 frame I have sitting around. I have a very nice .224 blank, 20.5 inches long and .840 diameter to use for the barrel, is is a slow twist 1 in 16, with 4 lands and groves so it needs to be a fast light bullet round. Was considering a true .223 AI, or something simular, I think I need to stay with a small case diameter size because of the thickness of the barrel at the breach end, I am not knowledgable about the thickness required at the chamber end of a barrel. Any thoughts on chambering for this would be appreciated. I will start the stubbing process again now, the chambering will be the last thing. Larry