You might have a .62 caliber Green Mountain Barrel Co. smoothbore on that stock. If the stock was originally for a Big Bore, it would handle that barrel. They are a 20 gauge technically. They will shoot a .600 roundball and are pretty accurate to 40 yards. I used to have one, and there are little to no markings on the barrel itself. That is an excellent barrel. You can also load a 20 gauge wad and shoot bird shot out of it.