I do not use it yet as I have not built it yet but I have breeched and drummed a 9mm (.355) full tapered slim octagon smoothbore barrel off of a Spanish cheapo Kentucky rifle. I understand 9mm smooth barrel guns are popular in Europe (I guess for shooting starlings and packrats). The barrel is 29" long and tapers from 13/16" atf to 5/8" at the muzzle. This I plan to fabricate into a small back action percussion half stock 'monkey' gun or even a long barreled 'specimen' gun with a pistol grip stock. In have no idea how well this thing will work, being an open choke, but I bet it will be fun, and run Parks and Wildlife dept. crazy trying to pigeon hole it into an obscure classification of legalese. I have in my tuteledge built ml shotguns in the 41-45 caliber range and was surprised at their power. but this will be a new low, so to speak. It is as small a bore as I would recommend for 'little edibles' as Dr. Sam Fadala would say.