What is the difference between the gauge and caliber?

Answer 1

Caliber is the measure of th internal diameter of the barrel in inches- a .30 caliber gun fires a bullet that is about 30/100ths of an inch across. European guns are usually measured in millimeters- a 9mm fires a 9mm diameter bullet. Bigger number equals bigger bullet. GAUGE is an older term used to measure the internal diameter of a shotgun barrel. It came from the number of round lead balls that fit the barrel that add up to one pound. So 20 balls in 20 gauge weigh one pond, 12 balls in 12 g weigh one pound, etc. SMALLER the gauge, bigger the barrel. The .410 shotgun is the exception- that is really .410 caliber.