Unfortunately there is no standard. We still have the .45-70, and the .250-3000.
Hum the 50 bmg is. 502" in dial. How is that not 1/2"?c3shooter said:do NOT assume that the system makes sense. Much of the naming was done by marketing departments after a 3 martini lunch. .50 Browning Machine Gun is NOT .50 inches in diameter. There are a handful of 9mms - many of which are NOT 9mm. .32 Short Colt and .32 S&W are not the same diameter. Neither is .22 LR and .22 Magnum. And yes, Americans measure a bore one way, Europeans another.
Why ask why? Drink Bud Dry.
wrong..........straight from a .50bmg barrel maker