If you're SB won't fit by a little, it could be made for a Colt SAA. But even then, you should be able to force the SB into it. If it's that close, you could soak it in the kitchen sink (add just a couple drops of dish soap) and stretch it. Put the SB in a plastic bag and work it into the holster and leave it until it gets mostly dry. If it fits at the top but won't take the barrel/ejector housing, it's likely made for a double action. I have made those fit also with the above method. If still too small all over, likely it was made for a 9 1/2" Single Six or Colt scout/New Frontier .22. 44 Man.