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.410 bore, commonly misnamed the .410 gauge, is the smallest caliber of shotgun shell commonly available. It has similar base dimensions to the .45 Colt revolver cartridge (though the .410 is significantly longer, up to 3 inches in length), allowing many single-shot firearms and some revolvers chambered in that caliber to fire shot without any modifications.
The .410 bore is a relative latecomer in shotgun sizes. It appears to have become popular around 1900. Some suspect that this shotgun arose from converted rifles of a similar bore diameter. The first ammunition was two inches (5.08 cm) in length, compared with the modern 2.5 and 3.0 inch sizes.
Pronounced four-ten, the .410 shotgun is a bore and not a gauge because the barrel diameter is .410 inches (10.4 mm); a true gauge is a measurement of the number of lead balls of bore diameter that constitute a pound (454 grams). The .410, when measured by gauge, would be around 67 or 68 gauge,, not the sometimes mistakenly assigned 36 gauge. A true gauge measuring .410 would have a 2.25 inch (57 mm) bore; a 410 gauge would measure .225 inches (5.7 mm). In the US, the .410 is the only popular shotgun cartridge named by bore rather than gauge, though it is often referred to as a four-ten gauge. In the United Kingdom and other English speaking countries, all shotgun sizes are called bore, whether measured by gauge or bore diameter.
As the smallest of traditional shotgun sizes, .410 bore guns throw the least weight of shot. This results in a very low recoil, so the .410 is often chosen for young shooters, who might have problems with a heavier recoiling shotgun. Some shooters however do discourage the use of the .410 as an introduction for young shooters, both because the negligible recoil does not familiarize the beginners with the heavier recoil of larger cartridges such as the 12 gauge, and because of the difficulty in hitting moving targets with the small charge of shot used by the .410.
Some competitive shooters choose the .410 bore because of the challenge it presents; .410 bore guns generally have full chokes to form a tight pattern with the small load of shot, and this makes hitting moving targets very challenging. By using sub-gauge inserts, a 12 gauge break open action can be temporarily converted down as far as a .410 bore to provide additional challenge when training, or to handicap the shooter.
The .410 bore is considered far inferior to the traditional 12 gauge shotshell for defensive use, though a number of companies market defensive guns chambered in .410, such as the Mossberg 500 Home Security model. Defensive ammunition is harder to find, since most .410 bore shells are loaded with birdshot. American Derringer and Winchester market .410 bore 000 buckshot with 5 pellets in 3 inch and 3 in 2.5 inch shells, compared to the 10 pellets in a 3 inch 12 gauge, or twelve 00 pellets in a 2¾ inch 12 gauge. With slug loads, the .410 bore compares better, with about 750 ft·lbf (1,020 J) of muzzle energy, comparable to a .44 Magnum handgun loading.
The small size of the .410 bore makes it popular for use in compact firearms carried for emergency use. Commonly these are combination guns, with a .22 Hornet or .22 rimfire rifle barrel mounted over a .410 bore shotgun barrel. The most famous of these is the M6 survival rifle made by Springfield Armory, Inc. for the US Air Force, and a number of copies are made by other makers. The original has a 14 inch barrel, the same length as the stock, and folds in half for storage, making a compact package. With the short barrel, this is classified as a sawed-off shotgun in the United States, so 18.5 inch barrelled models are made for civilian sales, as well as a 16 inch pistol version in .22 over .45 Colt. Special flare cartridges in .410 were issued with the USAF model.
The Thompson Center Arms 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 18 inch minimum barrel length.
The fact that the .410 bore shell fits in a .45 Colt chamber has resulted in some unusual applications. While shotguns are often limited in minimum length, a firearm chambered in .45 Colt, such as the Contender pistol, is not defined as a shotgun even though it can chamber shotgun shells. American Derringer has long offered .45 Colt/.410 bore Derringers, and recently Taurus and Magnum Research both began to offer revolvers with extended cylinders, chambered for .45 Colt but long enough to hold .410 shells as well. Magnum Research’s is an expensive single-action model in their BFR (Biggest, Finest Revolver) line, while the inexpensive Taurus model is similar in price to their other double-action revolvers.
- ^ Barnes, Frank C. (2006) . Skinner, Stan. ed. Cartridges of the World (11th Edition ed.). Iola, WI, USA: Gun Digest Books. p. 502. ISBN 0-89689-297-2.
- ^ Chuck Hawks’ updated rec.guns FAQ on defensive ammunition
- ^ Winchester .410 buckshot
- ^ American Derringer .410 buckshot
- ^ Federal .410 bore slug #F412RS, 762 ft·lbf (1,033 J), vs. .44 Magnum #P44HS1, 780 ft·lbf (1,058 J)
- ^ S. P. Fjestad. Blue Book of Gun Values, 13th Ed.. Blue Book Publications.
- ^ “G2 Contender Pistols“. Retrieved on 2007-09-20.
- ^ American Derringer model 1