20-gauge shotgun
The 20-gauge shotgun, also known as "20-bore", is a type of smooth-bore shotgun that fires a shell that is smaller in caliber (.615 in (15.6 mm)) than a 12-gauge shotgun (.729 in (18.5 mm)). It is often used by beginning shooters for target practice and for hunting small game.
| 20 gauge | ||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
 3 23⁄4" 20-gauge shells (right) loaded with number 7 1/2 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 | ||||||||||||||||||||||||
| Bullet diameter | .615" (15.62 mm) | |||||||||||||||||||||||
| Shoulder diameter | .684 in (17.37 mm) | |||||||||||||||||||||||
| Base diameter | .697 in (17.70 mm) | |||||||||||||||||||||||
| Rim diameter | .766 in (19.46 mm) | |||||||||||||||||||||||
| Rim thickness | .0484 in (1.23 mm) | |||||||||||||||||||||||
| Case length | 2.76 in (70.10 mm) | |||||||||||||||||||||||
| Primer type | Shotshell Primer | |||||||||||||||||||||||
| Maximum pressure | 12,000 psi (83 MPa) | |||||||||||||||||||||||
| Ballistic performance | ||||||||||||||||||||||||
| ||||||||||||||||||||||||
Description
It takes 20 lead balls of the diameter of a 20-gauge shotgun bore to equal one pound, while it only takes 12 lead balls of the diameter of a 12-gauge shotgun bore to equal the same weight. A 20-gauge shotgun is more suitable for hunting certain types of game or for some hunters because it recoils less, and the guns weigh less and may be smaller.
Regarding the yellow body tube color 20-gauge ammunition usually has, it has been reserved in SAAMI documentation saying "SAAMI has reserved yellow for 20-gauge ammunition" "This ammunition shall have a body tube that is primarily yellow" "Yellow shall not be used for any other gauge/bore shotshell body" "No other recommendations are made as to the color of service body tubes for other gauges/bores"[1]
Specifications
20-gauge shotguns are especially suitable for hunting game birds such as quail, grouse, turkey, and other game when using shot shells. A 20-gauge can also shoot slugs and buckshot and thereby become an effective deer-hunting gun. While shotguns loaded with slugs are generally less accurate than rifles, full-power shells often have better stopping power at short range due to the large mass of the projectile.[2]
Performance
A usually lower weapon weight makes a 20-gauge appropriate for young, elderly, or weaker shooters who may have a difficult time carrying, aiming, and firing a larger shotgun. In addition, 20-gauge shotguns generally have less recoil than 10-, 12-, or 16-gauge versions on average, when comparing standard hunting shells, due to the lower projectile payload. These parameters make the 20-gauge more pleasant to use on extended hunting trips for small game or upland birds, even for people capable of firing magnum-power 12-gauge hunting rounds.
It should be noted, however, that full-power 20-gauge shells fired from a light 4.5 lb (2.0 kg) weapon will have more felt recoil than reduced-recoil 12-gauge shells fired from a heavy 8 lb (3.6 kg) weapon.