The Gauge or bore of a shotgun is a unit of measurement used to express the diameter of the barrel. The gauge or bore of the inside diameter of a barrel corresponds with the number of identical solid spheres that can be made from a pound of lead. A pump-action, a Remington 870, two semi-automatic action Remington 1100 shotguns, 20 boxes of shotgun shells, a clay trap, and three boxes of clay pigeons. ... The former Weights and Measures office in Middlesex, England. ... DIAMETER is an AAA protocol (Authentication, Authorization and Accounting) succeeding its predecessor RADIUS. // The name is a pun on the RADIUS protocol, which is the predecessor (a diameter is twice the radius). ... This article does not cite its references or sources. ... The pound (abbreviations: lb or, sometimes in the United States, #) is a unit of mass in a number of different systems, including various systems of units of mass that formed part of English units, Imperial units, and United States customary units. ... For Pb as an abbreviation, see PB. General Name, Symbol, Number lead, Pb, 82 Chemical series Post-transition metals or poor metals Group, Period, Block 14, 6, p Appearance bluish gray Standard atomic weight 207. ...

The term also related to the measurement of black powder cannon, which were also measured by the weight of their round iron shot; a 6 pounder, for example, would fire a 6 pound (2.7 kg) spherical cast iron ball, which gave a bore diameter of about 3.6 inches (9.1 cm). Black powder was the original gunpowder and practically the only known propellant and explosive until the middle of the 19th century. ... Not to be confused with Canon. ... Cast iron usually refers to grey cast iron, but can mean any of a group of iron-based alloys containing more than 2% carbon (alloys with less carbon are carbon steel by definition). ...

Calculating gauge

An n-gauge diameter means that n balls of lead (density 11.352 g/cm³) with that diameter weigh one pound (453.5924 g). Therefore an n-gauge shotgun has a bore diameter of approximately

Gauge in use

From left to right: 9 mm Luger Parabellum, .40 S&W, .45 ACP, 5.7x28mm, 5.56x45mm NATO, .300 Winchester Magnum, and a 2.75-inch and 3-inch 12 gauge.

Since shotguns were not originally intended to fire solid projectiles, but rather a compressible mass of shot, the actual diameter of the bore varies quite a bit. The fact that most shotgun bores are not cylindrical also causes deviations from the ideal bore diameter. Image File history File links Download high-resolution version (2736x1540, 442 KB) This is a line-up of pistol and rifle cartridges. ... Image File history File links Download high-resolution version (2736x1540, 442 KB) This is a line-up of pistol and rifle cartridges. ... This article does not cite any references or sources. ... The . ... .45 ACP cartridges .45 redirects here. ... The 5. ... U.S. Military 5. ... .300 Winchester Magnum (known as . ...

The chamber of the gun is larger, to accommodate the thickness of the shotshell walls, and a "forcing cone" in front of the chamber reduces the diameter down to the bore diameter. The forcing cone can be as short as a fraction of an inch, or as long as 4 inches on some guns. At the muzzle end of the barrel, the choke can constrict the bore even further, so measuring the bore diameter of a shotgun is not a simple process, as it must be done away from either end. A pump-action, a Remington 870, two semi-automatic action Remington 1100 shotguns, 20 boxes of shotgun shells, a clay trap, and three boxes of clay pigeons. ...

Shotgun bores are commonly "overbored" or "backbored", meaning that most of the bore (from the forcing cone to the choke) is slightly larger than the value given by the formula. This is claimed to reduce felt recoil and improve patterning. The recoil reduction is due to the larger bore producing a slower acceleration of the shot, and the patterning improvements are due to the larger muzzle diameter for the same choke constriction, which results in less shot deformation. A 12 gauge shotgun, nominally 0.729 inches, can range from a tight 0.720 inches to an extreme overbore of 0.800 inches. Some also claim an increased velocity with the overbored barrels, up to 50 feet per second, which is due to the larger swept area of the overbored barrel. Once only found in expensive custom shotguns, overbored barrels are now becoming common in mass marketed guns. Aftermarket backboring is also commonly done to reduce the weight of the barrel, and move the center of mass backwards for a better balance. Factory overbored barrels generally are made with a larger outside diameter, and will not have this reduction in weight--though the factory barrels will be tougher, since they have a normal barrel wall thickness. In physics, the center of mass of a system of particles is a specific point at which, for many purposes, the systems mass behaves as if it were concentrated. ...

Note: Slugs should not be fired from overbored barrels, as the slug may be incapable of obturating to fill the oversized bore, which can result in very inconsistent accuracy.

For other meanings, see Slug (disambiguation) A slug is a term used for a solid ballistic projectile. ... Obturate means to block or obstruct. ...

Sizes in use

Certain sizes are more common than others; 12-gauge is probably the most common size. The 20-gauge is popular with shooters who are uncomfortable with the weight and recoil of a 12 gauge gun. The next most popular size is the .410, which is not a gauge, but a caliber. 10, 16 and 28 gauges, while less common, are still readily available. Shotguns larger than 10-gauge are rarely manufactered nowadays; guns like the KS-23, a 4-gauge, are very few in number. The word calibre (British English) or caliber (American English) designates the interior diameter of a tube or the exterior diameter of a wire or rod. ... KS-23 A 23mm Russian shotgun firing the Barricade slug, also used to launch various nonlethal grenade-related weapons. ...

Conversion guide

A table showing the various shotgun gauge sizes with weights. The bores marked ^* are found in punt guns and rare weapons only. The .410 bore is an exception; it is an actual bore size, not a gauge. If the .410 were measured traditionally, it would be 67½ gauge. A punt gun is a type of extremely large shotgun used in the 19th and 20th centuries for shooting large numbers of waterfowl for commercial harvesting operations. ... . ...

See also

• Smoothbore
• Gauge
• Caliber

Smoothbore refers to a firearm which does not have a rifled barrel. ... Look up Gauge in Wiktionary, the free dictionary. ... The word calibre (British English) or caliber (American English) designates the interior diameter of a tube or the exterior diameter of a wire or rod. ...

External links

• Pacific Tool and Gauge