Contender pistols are commonly encountered with a special .45 Colt/.410 bore barrel. The barrel is rifled for the .45 Colt, but has a special choke and vent rib to make it function as a shotgun. Due to the rifled barrel, the assembled firearm is considered a rifle or pistol (depending on barrel length) and thus is not subject to the National Firearms Act's minimum barrel length. Nonetheless, possession of a Thompson Center Arms .45/.410 pistol barrel is illegal in California, for both dealers and individuals, and such a barrel may not legally be shipped into the state, or even taken into California for a hunting trip, by reason of it being classified as a short barreled shotgun (SBSG) when used with a Contender receiver. American Derringer has long offered .45 Colt-.410 bore Derringers. Bond Arms also offers various Derringer models which chamber both .45 Colt cartridges and .410 shotshell. Also, Taurus, Magnum Research, and Smith & Wesson offer revolvers with extended cylinders, long enough to hold .410 shells as well. Magnum Research offers a single-action revolver in their BFR (big frame revolver) line, while the Taurus Judge is similar in price to their other double-action revolvers, with the Raging Judge model capable of chambering and firing the .454 Casull cartridge. The Smith & Wesson Governor is a double-action revolver also capable of firing .45 Colt as well as .45 ACP cartridges with the aid of moon clips. The discontinued MIL Thunder 5 is also chambered in .410-bore. Over the years, a large number of devices have been made that will convert larger-gauge shotguns to accept .410 shotgun shells. Capacity, compared to other gauges Most shotgun cartridges are measured in terms of shotgun gauge. Shotgun gauge is determined by the weight of a round lead ball that is sized to fit into its barrel. For example, the barrel of a 12-gauge shotgun is equal to the diameter of a one-twelfth/pound lead ball (0.729 in) and a 20-gauge can fit a one-twentieth/pound lead ball (0.615 in). Using this method a .410 bore is equivalent to a (hypothetical) 67-gauge. References External links The Shotgun Report review of the Remington 870 in 28 gauge and .410 bore The .410 Bore by Chuck Hawks Shotgun shells