Originally Posted By: RARiddell
There is a 7 on the short rib and 13 stamped on the tube, but I think thats a part of the proofs.


The 13 would be part of the proof. Must be a 12ga gun but made underbored, with 13ga bore diameters. Not at all unusual, and it doesn't mean you can't shoot 12ga shells. Simply means that the original bore diameter, rather than being the standard 12ga .729", is .719".