Thegauge(in American English or more commonly referred to asborein British English) of afirearmis a unit of measurement used to express the inner diameter (bore diameter) of thebarrel.
| Gauge | |
|---|---|
 | |
| Type | Shotgun |
| Place of origin | Various |
Gauge is determined from the weight of a solid sphere of lead that will fit the bore of the firearm and is expressed as themultiplicative inverseof the sphere's weight as a fraction of a pound, e.g., a one-twelfth pound lead ball fits a 12-gauge bore. Therefore with a 12-gauge, it would take 12 balls of lead of the same size as the 12 gauge shotgun's inner bore diameter to weigh 1 pound (454 grams).[1]The term is related to the measurement ofcannons,which were also measured by the weight of their ironround shot;aneight-pounderwould fire an 8 lb (3.6 kg) ball.
Gauge is commonly used today in reference toshotguns,though historically it was also used in largedouble rifles,which were made in sizes up to2 boreduring their heyday in the 1880s, being originally loaded with black powder cartridges. These very large rifles, called "elephant guns",were intended for use primarily in Africa and Asia for hunting large dangerous game.
Gauge is commonly abbreviated as "ga.", "ga", or "G".
Calculating gauge
editAnn-gauge diameter means that a ball of lead (density 11.34 g/cm3or 0.4097 lb/in3) with that diameter has a mass equal to1/npart of the mass of theinternational avoirdupois pound(approx. 454 grams), that is, thatnsuch lead balls could be cast from a pound weight of lead. Therefore, ann-gauge shotgun orn-bore rifle has a bore diameter (in inches) of approximately
![{\displaystyle d_{n}=2{\sqrt[{3}]{{\frac {3}{4\pi }}{\frac {1\mathrm {~lb} /n}{0.4097\mathrm {~lb/in^{3}} }}}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/0928ab47102d9f4aa3b8b3d53afaa2c4f6b07b27)
Explanation:
- Divide 1 pound bynto find the mass of each one of the balls
- Divide it by 0.4097 lb/in3(density of lead) to find the volume of each ball
- Multiply it by3/4and divide it byπ,then find itscube root(rearranged from thevolume of a sphereequation) to find the radius of each ball
- Multiply it by 2 to change from radius to diameter
This simplifies to the following formula for the internal diameter of the barrel of ann-gauge shotgun:
![{\displaystyle d_{n}=1.67/{\sqrt[{3}]{n}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/1b8181709e4daca3d06a5eb9f923070761e44f2b)
in inches, or
![{\displaystyle d_{n}=42.4/{\sqrt[{3}]{n}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/2310a134d924bfd00fcb9e83622fc4ef4e2b4b55)
in millimeters.
Likewise, given the diameter in inches, the gauge is
The gauge of firearms is determined by: 1 pound/gauge = weight of lead sphere.Caliberof the bore is then measured.[2][full citation needed]
| 1 Pound / gauge = weight of lead sphere | Diameter of bore is then measured | ||
|---|---|---|---|
| gauge | pounds | mm | inches |
| 0.25 | 4 | 67.34 | 2.651 |
| 0.5 | 2 | 53.45 | 2.103 |
| 0.75 | 1+1/3 | 46.70 | 1.838 |
| 1 | 1 | 42.42 | 1.669 |
| 1.5 | 2/3 | 37.05 | 1.459 |
| 2 | 1/2 | 33.67 | 1.326 |
| 3 | 1/3 | 29.41 | 1.158 |
| 4 | 1/4 | 26.72 | 1.052 |
| 5 | 1/5 | 24.80 | 0.976 |
| 6 | 1/6 | 23.35 | 0.919 |
| 6.278 | 1/6.278 | 23.00 | 0.906 |
| 7 | 1/7 | 22.18 | 0.873 |
| 8 | 1/8 | 21.21 | 0.835 |
| 9 | 1/9 | 20.39 | 0.803 |
| 10 | 1/10 | 19.69 | 0.775 |
| 11 | 1/11 | 19.07 | 0.751 |
| 12 | 1/12 | 18.53 | 0.729 |
| 13 | 1/13 | 18.04 | 0.710 |
| 14 | 1/14 | 17.60 | 0.693 |
| 15 | 1/15 | 17.21 | 0.677 |
| 16 | 1/16 | 16.83 | 0.663 |
| 17 | 1/17 | 16.50 | 0.650 |
| 18 | 1/18 | 16.19 | 0.637 |
| 19 | 1/19 | 15.90 | 0.626 |
| 20 | 1/20 | 15.63 | 0.615 |
| 21 | 1/21 | 15.37 | 0.605 |
| 22 | 1/22 | 15.13 | 0.596 |
| 23 | 1/23 | 14.91 | 0.587 |
| 24 | 1/24 | 14.70 | 0.579 |
| 25 | 1/25 | 14.50 | 0.571 |
| 26 | 1/26 | 14.31 | 0.564 |
| 27 | 1/27 | 14.12 | 0.556 |
| 28 | 1/28 | 13.97 | 0.550 |
| 29 | 1/29 | 13.79 | 0.543 |
| 30 | 1/30 | 13.64 | 0.537 |
| 31 | 1/31 | 13.49 | 0.531 |
| 32 | 1/32 | 13.36 | 0.526 |
| 33 | 1/33 | 13.20 | 0.520 |
| 34 | 1/34 | 13.08 | 0.515 |
| 35 | 1/35 | 12.95 | 0.510 |
| 36 | 1/36 | 12.85 | 0.506 |
| 37 | 1/37 | 12.73 | 0.501 |
| 38 | 1/38 | 12.62 | 0.497 |
| 39 | 1/39 | 12.50 | 0.492 |
| 40 | 1/40 | 12.40 | 0.488 |
| 41 | 1/41 | 12.30 | 0.484 |
| 42 | 1/42 | 12.19 | 0.480 |
| 43 | 1/43 | 12.16 | 0.477 |
| 44 | 1/44 | 12.01 | 0.473 |
| 45 | 1/45 | 11.91 | 0.469 |
| 46 | 1/46 | 11.84 | 0.466 |
| 47 | 1/47 | 11.80 | 0.463 |
| 48 | 1/48 | 11.66 | 0.459 |
| 49 | 1/49 | 11.58 | 0.456 |
| 50 | 1/50 | 11.51 | 0.453 |
| 51 | 1/51 | 11.43 | 0.450 |
| 52 | 1/52 | 11.35 | 0.447 |
| 53 | 1/53 | 11.30 | 0.445 |
| 54 | 1/54 | 11.23 | 0.442 |
| 55 | 1/55 | 11.15 | 0.439 |
| 56 | 1/56 | 11.07 | 0.436 |
| 57 | 1/57 | 11.02 | 0.434 |
| 58 | 1/58 | 10.95 | 0.431 |
| 59 | 1/59 | 10.90 | 0.429 |
| 60 | 1/60 | 10.85 | 0.427 |
| 61 | 1/61 | 10.77 | 0.424 |
| 62 | 1/62 | 10.72 | 0.422 |
| 63 | 1/63 | 10.67 | 0.420 |
| 64 | 1/64 | 10.59 | 0.417 |
| 65 | 1/65 | 10.54 | 0.415 |
| 66 | 1/66 | 10.49 | 0.413 |
| 67 | 1/67 | 10.44 | 0.411 |
| 67.62 | 1/67.62 | 10.41 | 0.410 |
| 68 | 1/68 | 10.40 | 0.409 |
| 69 | 1/69 | 10.34 | 0.407 |
| 70 | 1/70 | 10.29 | 0.405 |
| 71 | 1/71 | 10.24 | 0.403 |
| 72 | 1/72 | 10.20 | 0.401 |
| 73 | 1/73 | 10.16 | 0.400 |
| 74 | 1/74 | 10.10 | 0.3978 |
| 75 | 1/75 | 10.05 | 0.3960 |
| 76 | 1/76 | 10.01 | 0.3942 |
| 77 | 1/77 | 9.97 | 0.3925 |
| 78 | 1/78 | 9.93 | 0.3908 |
| 79 | 1/79 | 9.86 | 0.3892 |
| 80 | 1/80 | 9.84 | 0.3876 |
| 81 | 1/81 | 9.80 | 0.3860 |
| 82 | 1/82 | 9.76 | 0.3844 |
| 83 | 1/83 | 9.72 | 0.3828 |
| 84 | 1/84 | 9.67 | 0.3813 |
| 85 | 1/85 | 9.65 | 0.3798 |
| 86 | 1/86 | 9.61 | 0.3783 |
| 87 | 1/87 | 9.57 | 0.3769 |
| 88 | 1/88 | 9.54 | 0.3754 |
| 89 | 1/89 | 9.50 | 0.3740 |
| 90 | 1/90 | 9.46 | 0.3726 |
| 91 | 1/91 | 9.43 | 0.3713 |
| 92 | 1/92 | 9.40 | 0.3699 |
| 93 | 1/93 | 9.36 | 0.3686 |
| 94 | 1/94 | 9.33 | 0.3673 |
| 95 | 1/95 | 9.30 | 0.3660 |
| 96 | 1/96 | 9.26 | 0.3647 |
| 97 | 1/97 | 9.23 | 0.3634 |
| 98 | 1/98 | 9.20 | 0.3622 |
| 99 | 1/99 | 9.17 | 0.3610 |
| 100 | 1/100 | 9.14 | 0.3598 |
Bore sizing
editSince shotguns were not originally intended to fire solid projectiles, but rather a compressible mass of shot, the actual diameter of the bore can vary. The fact that most shotgun bores are not cylindrical also causes deviations from the ideal bore diameter.
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 a few inches on some guns. At the muzzle end of the barrel, thechokecan 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.
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 18.5 mm (0.73 in), can range from a tight 18 mm (0.71 in) to an extreme overbore of 20 mm (0.79 in). Some also claim an increased velocity with the overbored barrels, up to 15 m/s (49 ft/s), which is due to the larger swept volume 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 thecenter of massbackward 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.
Firingslugsfrom overbored barrels can result in very inconsistent accuracy, as the slug may be incapable ofobturatingto fill the oversized bore.
Gauges in use
edit
The six most common shotgun gauges, in descending order of size, are the 10 gauge, 12 gauge, 16 gauge,20 gauge,28 gauge, and.410 bore.[3]By far the most popular is the 12 gauge,[3]particularly in the United States.[4]The 20-gauge shotgun is the next most popular size, being favored by shooters uncomfortable with the weight and recoil of a 12-gauge gun, and is popular forupland game hunting.The next most popular sizes are the.410 bore and the 28 gauge. The least popular sizes are the 10 gauge and the 16 gauge, while far less common than the other four gauges, they are still commercially available.[citation needed][5]
Shotguns and shells exceeding 10 gauge, such as the 8 gauge, 6 gauge, 4 gauge, and 2 gauge are historically important in the United Kingdom and elsewhere inmainland Europe.Today, they are rarely manufactured. These shells are usuallyblack powderpaper or brass cartridges, as opposed to modernsmokeless powderplastic or wax cartridges.
The 18, 15, 11, 6, 3, and 2 gauge shells are the rarest of all;[6]owners of these types of rare shotguns will usually have their ammunition custom loaded by a specialist in rare and custom bores. The 14 gauge has not been loaded in the United States since the early 20th century, although the2+9⁄16-inch (65 mm) hull is still made in France.[6]The very small 24 and 32 gauges are still produced and used in some European and South American countries.Punt guns,which use very large shells, are rarely encountered.
Also seen in limited numbers aresmoothborefirearms in calibers smaller than.360 such as.22 Long Rifle(UK No. 1 bore) and9mm Flobertrimfire(UK No. 3 bore), designed for short-range pest control andgarden guns.The No. 2 bore (7 mm) has long been obsolete. All three of these rimfires are available in shot and BB-cap.[7][8]
Gauge and shot type
edit
The 10 gauge narrowly escaped obsolescence when steel and othernontoxic shotbecame required forwaterfowl hunting,since the larger shell could hold the much larger sizes of low-density steel shot needed to reach the ranges necessary for waterfowl hunting. The move to steel shot reduced the use of 16 and 20 gauges for waterfowl hunting, and the shorter,2+3⁄4-inch (70 mm), 12-gauge shells as well. However, the3+1⁄2-inch (89 mm) 12-gauge shell, with its higherSAAMIpressure rating of 14,000 psi (97 MPa) compared to standard2+3⁄4-inch (70 mm) and 3-inch (76 mm) 12-gauge shells with their lower pressure rating of 11,500 psi (79 MPa), began to approach the performance of the3+1⁄2-inch (89 mm) 10-gauge shells with a pressure rating of 11,000 psi (76 MPa).[9]Newer nontoxic shots, such asbismuthortungsten-nickel-iron alloys, and even tungsten-polymerblends, regain much or all of the performance loss, but are much more expensive thansteelorleadshot.[10]However, laboratory research indicates that tungsten alloys can actually be quite toxic internally.[11]
Bore sizes used in the United Kingdom
editLegend: left side is the bore size, right side is the case length
- 2 bore:3+1⁄2in (89 mm)
- 4 bore:3+1⁄4,4 in (83, 102 mm)
- 6 bore
- 8 bore:3,3+1⁄4,3+3⁄4,4 in (76, 83, 95, 102 mm)
- 10 bore:2+9⁄16,2+5⁄8,2+7⁄8,3,3+1⁄4,3+1⁄2in (65, 67, 73, 76, 83, 89 mm)
- 12 bore:1+3⁄4,2,2+1⁄4,2+1⁄2,2+3⁄4,3,3+1⁄2in (44, 51, 57, 64, 70, 76, 89 mm)
- 14 bore:2+1⁄2in (64 mm)
- 16 bore:2+1⁄2,2+9⁄16,2+5⁄8,2+3⁄4,3 in (64, 65, 67, 70, 76 mm)
- 20 bore:2+1⁄2,2+3⁄4,3,3+1⁄2in (64, 70, 76, 89 mm)
- 24 bore:2+1⁄2in (64 mm)
- 28 bore:2+1⁄2,2+3⁄4,3 in (64, 70, 76 mm)
- 32 bore:2+1⁄2in (64 mm)
- .410 bore:2,2+1⁄2,3 in (51, 64, 76 mm)
- .360 bore:1+3⁄4in (44 mm)
- 9 mm (No. 3 bore) short rimfire, 9 mm (No. 3 bore) long rimfire
- 7 mm (No. 2 bore) rimfire
- 6 mm (No. 1 bore) short rimfire, 6 mm (No. 1 bore) long rimfire
Conversion guide
edit
The table below lists various gauge sizes with weights. The bores marked*are found in punt guns, obsolete, or rare weapons only. However, 4 gauge was sometimes found used inblunderbussguns made for coach defense and protection against piracy. The.410and23 mmare exceptions; they are actual bore sizes, not gauges. If the.410 bore and 23 mm diameters were measured using more traditional means, they would be equivalent to 67.62 gauge (.410 bore) and 6.278 gauge (23 mm), respectively.
| Gauge (bore) |
Diameter | Weight of unalloyed (pure) lead ball | |||
|---|---|---|---|---|---|
| (mm) | (in) | grams | ounces | grains | |
| AA* | 101.60 | 4.000 | 6,225.52 | 219.6 | 96,080 |
| A1/2* | 76.20 | 3.000 | 2,626.39 | 92.64 | 40,530 |
| 0.25* | 67.34 | 2.651 | 1,814.36 | 64.000 | 28,000 |
| 0.5* | 53.45 | 2.103 | 907.18 | 32.000 | 14,000 |
| A* | 50.80 | 2.000 | 778.19 | 27.45 | 12,010 |
| 0.75* | 46.70 | 1.838 | 604.80 | 21.336 | 9,328 |
| 1* | 42.42 | 1.669 | 453.59 | 16.000 | 7,000 |
| B1/2* | 38.10 | 1.500 | 328.3 | 11.58 | 5,066 |
| 1.5* | 37.05 | 1.459 | 302.39 | 10.667 | 4,667 |
| 2* | 33.67 | 1.326 | 226.80 | 8.000 | 3,500 |
| 3* | 29.41 | 1.158 | 151.20 | 5.333 | 2,333 |
| 4* | 26.72 | 1.052 | 113.40 | 4.000 | 1,750 |
| B* | 25.40 | 1.000 | 97.27 | 3.43 | 1,501 |
| 5* | 24.80 | 0.976 | 90.72 | 3.200 | 1,400 |
| 6* | 23.35 | 0.919 | 75.60 | 2.667 | 1,166 |
| 6.278* | 23.00 | 0.906 | 72.26 | 2.549 | 1,114 |
| 7* | 22.18 | 0.873 | 64.80 | 2.286 | 1,000 |
| 8* | 21.21 | 0.835 | 56.70 | 2.000 | 875 |
| 9* | 20.39 | 0.803 | 50.40 | 1.778 | 778 |
| 10 | 19.69 | 0.775 | 45.36 | 1.600 | 700 |
| 11* | 19.07 | 0.751 | 41.24 | 1.454 | 636 |
| 12 | 18.53 | 0.729 | 37.80 | 1.333 | 583 |
| 13* | 18.04 | 0.710 | 34.89 | 1.231 | 538 |
| 14* | 17.60 | 0.693 | 32.40 | 1.143 | 500 |
| 15* | 17.21 | 0.677 | 30.24 | 1.067 | 467 |
| 16 | 16.83 | 0.663 | 28.35 | 1.000 | 438 |
| 17* | 16.50 | 0.650 | 26.68 | 0.941 | 412 |
| 18* | 16.19 | 0.637 | 25.20 | 0.889 | 389 |
| 20 | 15.63 | 0.615 | 22.68 | 0.800 | 350 |
| 22* | 15.13 | 0.596 | 20.62 | 0.728 | 319 |
| 24 | 14.70 | 0.579 | 18.90 | 0.667 | 292 |
| 26* | 14.31 | 0.564 | 17.44 | 0.615 | 269 |
| 28 | 13.97 | 0.550 | 16.20 | 0.571 | 250 |
| 32 | 13.36 | 0.526 | 14.17 | 0.500 | 219 |
| 36* | 12.85 | 0.506 | 12.59 | 0.444 | 194 |
| 40* | 12.40 | 0.488 | 11.34 | 0.400 | 175 |
| 67.62 | 10.41 | 0.410 | 6.71 | 0.237 | 104 |
Note: Use of this table for estimating bullet masses for historical large-bore rifles is limited, as this table assumes the use of round ball, rather than conical bullets; for example, a typical 4-bore rifle from circa 1880 used a 2,000-grain (4.57 oz; 129.60 g) bullet, or sometimes slightly heavier, rather than using a 4-ounce (110 g) round lead ball. (Round balls lose velocity faster than conical bullets and have much steeper ballistic trajectories beyond about 75 yards or 69 metres) In contrast, a 4-boreexpress rifleoften used a 1,500-grain (3.43 oz; 97.20 g) bullet wrapped in paper to keep lead buildup to a minimum in the barrel. In either case, assuming a 4-ounce (110 g) mass for a 4-bore rifle bullet from this table would be inaccurate, although indicative.
References
edit- ^Barnes, Frank C.; Woodard, W. Todd (2016).Cartridges of the world: a complete and illustrated reference for more than 1500 cartridges(15th ed.). Krause Publications. p. 629.ISBN978-1440246425.OCLC934886116.
- ^Fourten Shotgun Resources.
- ^abKrause, Angel."What Shotgun Gauge Should I Use for Hunting?".Outly.Retrieved27 November2021.
- ^Carter, Greg Lee (2002).Guns in American Society: An Encyclopedia.Santa Barbara, Calif.; Oxford: ABC-CLIO. p. 361.ISBN978-1-57607-268-4.
- ^Wintersteen, K. (2014, December 9). The decline of 10- & 16-gauge shotguns. Firearms News.https:// firearmsnews /editorial/decline-10-16-gauge-shotguns/78028
- ^abFrank C. Barnes (2009). Layne Simpson (ed.).Cartridges of the World(12th ed.).
- ^Clair Rees (March 2000)."Marlin's 'Garden Gun'—Model 25MG".Guns Magazine.Archivedfrom the original on 2008-04-29.Retrieved2008-05-08.
- ^Frank C. Barnes (2003). Stan Skinner (ed.).Cartridges of the World(10th ed.). Krause Publications.ISBN0-87349-605-1.
- ^Tom Roster is an independent ballistics consultant and author specializing in the design and testing of shotshell loads for U.S. shotshell and reloading components manufacturers. He is a court-recognized shotshell/shotgun expert witness. Tom was formerly, T. R. (2014, January 1). Important information about shotshell pressures. Shotgun Life.https:// shotgunlife /shotguns/tom-roster/important-information-about-shotshell-pressures.html
- ^Randy Wakeman (2007)."Why the 10 Gauge Shotgun Is Obsolete".chuckhawks. Archived fromthe originalon 2006-05-13.
- ^John Kalinich; et al. (2005)."Embedded weapons-grade tungsten alloy shrapnel rapidly induces metastatic high-grade rhabdomyosarcomas in F344 rats".Environmental Health Perspectives.113(6): 729–34.Bibcode:2005EnvHP.113..729K.doi:10.1289/ehp.7791.PMC1257598.PMID15929896.