Why are bullet and ammunition sizes metric?

Question

In the United States, the accepted standard of measurement for pretty much everything is based on the Imperial system. Efforts to change over to metric have spurred heated debate. So why is there no opposition to using millimetres to measure ammunition?

Answer 1

If a round was developed in Europe then it often has a metric name. the .177 is a US name

Answer 2

Not all of them are metric either, the 12.7 x 99mm BMG (Browning Machine Gun) round is more commonly known as the .50 BMG. Ditto the .357 Lapua Magnum and the .44 and .50 Magnum rounds.

N.B. NATO has a hand in those metric rounds, most notably the 5.56 × 45mm assault rifle round and the 7.62 x 51mm machine gun rounds, which are used in common by NATO countries, making it easier to share ammunition.

Answer 3

Because of the standardized use of ammunition within NATO. All countries in this organization uses the same ammo. The U.S. is the only country that uses a decimal of an inch, or SAE scale in everyday civilian ammo and is not on the metric bandwagon. (I'm not talking about the gauges of shotguns, just pistols and rifles.) Although we use the metric sizes for military ammo, all of them still have their SAE couterpart, for example: 5.56mm=.223; 7.62mm x 51mm=.308.

Answer 4

Caliber is the imperial measurement.
.22 caliber is just under a quarter of an inch wide
9mm obviously metric
Often the measurement used depends on where the ammunition or gun was originally designed.

Answer 5

Ever hear of a 44. caliber Magnum? Calibers aren't metric.

Answer 6

Because the US army uses metric. It has to to coordinate with NATO forces.

Answer 7

It's one of those things that is truely global in usage, so I guess it's just easier.