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Barrel length

Shotguns generally have longer barrels than modern rifles. Unlike rifles, however, the long shotgun barrel is not for ballistic purposes; shotgun shells use small powder charges in large diameter bores, and this leads to very low muzzle pressures (see internal ballistics) and very little velocity change with increasing barrel length. According to Remington, modern powder in a shotgun burns completely in 25 (9.8425 in) to 36 (14.173 in) cm barrels.

Since shotguns are generally used for shooting at small, fast moving targets, it is important to lead the target by firing slightly ahead of the target, so that when the shot reaches the range of the target, the target will have moved into the pattern.

Shotguns made for close ranges, where the angular speed of the targets is great (such as skeet or upland bird hunting), tend to have shorter barrels, around 24 to 28 inches (610 to 710 millimetres). Shotguns for longer range shooting, where angular speeds are small (trap shooting; quail, pheasant, and waterfowl hunting), tend to have longer barrels, 28 to 36 inches (910 mm). The longer barrels have more angular momentum, and will therefore swing more slowly but more steadily. The short, low angular momentum barrels swing faster, but are less steady. These lengths are for pump or semi-auto shotguns; break open guns have shorter overall lengths for the same barrel length, and so will use longer barrels. The break open design saves between 7.62 and 15.24 cm (3.00 and 6.00 in) in overall length, but in most cases pays for this by having two barrels, which adds weight at the muzzle. Barrels for shotguns have been getting longer as modern steels and production methods make the barrels stronger and lighter; a longer, lighter barrel gives the same inertia for less overall weight.

Shotguns for use against larger, slower targets generally have even shorter barrels. Small game shotguns, for hunting game like rabbits and squirrels, or shotguns for use with buckshot for deer, are often 56 to 61 cm (22 to 24 in).

Shotguns intended for all-round hunting are a compromise, but a 72 to 74 cm (28 to 29 in) barrel pump-action 12-gauge shotgun with a modified choke can serve admirably for use as one gun intended for general all-round hunting of small-game such as quails, rabbits, pheasants, doves, and squirrels in semi-open wooded or farmland areas in many parts of the eastern US (Kentucky, Indiana, Tennessee) where dense brush is less of a hindrance and the ability to have more reach is important. For hunting in dense brush, shorter barrel lengths are often preferred when hunting the same types of game.