I thought the heavy 12g went on a 10g frame?
You are correct in that I think, but rifle barrels will not fit. The barrel diameter is too small, the firing pin is too big, etc.
There is a post on this on the next page of the forum where
Mr. Guru Tim has answered this question. I'm merely parroting what I read.
I did handle a 10 ga. recently however, and put a transfer bar in it for a friend, and I know it is a different animal from the rifle recievers, and the smaller shotgun recievers as well.
I have a 357 barrel that mounts on an sb1 shotgun frame, along with a 20 ga. barrel. The 357's and 44's are ok as far as I know on the newer sb1 frames.