20-gauge shotgun
| 20 gauge | ||||||||||||||||||||||||
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| Three 23⁄4" 20-gauge shells (right) loaded with #71⁄2 birdshot. | ||||||||||||||||||||||||
| Type | Shotgun | |||||||||||||||||||||||
| Place of origin | United Kingdom | |||||||||||||||||||||||
| Production history | ||||||||||||||||||||||||
| Manufacturer | Various | |||||||||||||||||||||||
| Variants | 21⁄2" (63.5 mm) 23⁄4" (70 mm) 3" (76.2 mm) | |||||||||||||||||||||||
| Specifications | ||||||||||||||||||||||||
| Case type | Rimmed, straight | |||||||||||||||||||||||
| Bullet diameter | .615 in (15.6 mm) | |||||||||||||||||||||||
| Shoulder diameter | .684 in (17.4 mm) | |||||||||||||||||||||||
| Base diameter | .697 in (17.7 mm) | |||||||||||||||||||||||
| Rim diameter | .766 in (19.5 mm) | |||||||||||||||||||||||
| Rim thickness | .0484 in (1.23 mm) | |||||||||||||||||||||||
| Case length | 2.76 in (70 mm) | |||||||||||||||||||||||
| Primer type | Shotshell Primer | |||||||||||||||||||||||
| Maximum pressure | 12,000 psi (83 MPa) | |||||||||||||||||||||||
| Ballistic performance | ||||||||||||||||||||||||
| 
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The 20-gauge shotgun, also known as 20 bore or 20 gauge, is a type of smoothbore shotgun. 20-gauge shotguns have a bore diameter of .615 in (15.6 mm), while the 12-gauge has a bore diameter of .729 in (18.5 mm). 12-gauge and 20-gauge shotguns are the most popular gauges in the United States. The 20-gauge is popular among upland game hunters, target shooters, and skeet shooters.