Common shotgun gauges are 10 gauge,

12 gauge, 16 gauge, 20 gauge, and 28 gauge.

The smaller the gauge number, the larger

the shotgun bore. Gauge is determined by

the number of lead balls of size equal to the

exact diameter of the bore that it

takes to weigh one pound. For example,

it would take 12 lead balls with the same

diameter as a 12-gauge shotgun bore to

weigh one pound. Today, however, gauge

can be measured much the same way as

caliber by measuring the inside bore diameter.

 

The .410-caliber shotgun is the only

exception to the gauge designation

for shotguns. It has an actual bore

diameter of 410/1000ths of an inch,

which is approximately equivalent to

a 67½ gauge.

Each gauge of shotgun shoots only

cartridge of the same gauge.

For example, 12-gauge cartridges

are used only in 12-gauge guns.

The gauge of a shotgun is usually marked

on the rear of the barrel, and the

gauge of a cartridge is marked on the

cartridge as well as on the factory box.