Ed, as Busta pointed out, the SB2 slug gun frame is different than the SB2 rifle frame, I've only seen one, it had the same matte finish as the rimfires, not the gloss blued look of the rifle SB2 frames. Another difference, I think :roll: , is the 12ga is a bored out 10ga barrel which is bigger in diameter than the rifle barrels, hence the reason they can't/won't fit rifle barrels to it, even if it has the higher strength which I doubt it does, it's the same material as the SB1 frame, just not the same heat treatment as rifle frames.....if that makes any sense, just making a sorta uneducated guess!!
Tim