h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

Why are weapons such odd calibres? Imperial/Metric notwithstanding, why is ammunition sized 7.62mm, 5.56mm etc? Why not 5mm, 10mm? On larger calibre weapons it seems to be clearer; 0.5", 40mm, 4.5" etc.

I presume there's a good reason for this?

http://en.wikipedia.org/wiki/Caliber

came up when I googled

Hmm, thanks But it doesn't really explain *why* such odd sizes are used.

I'd tell you, but then I'd have to shoot you.

RF

Originally bores were measured in fractions of an inch - now we fight globally on a regular basis these measurement have been converted into metric.

7.62mm = 0.3 inch, for example.

RF

That explains the metric/imperial, but not the odd sizes. For instance in WWII the US used .30 calibre whereas we used .303.

Who decided to use rounds of just under a third of an inch?

possibly so the enemy couldn't capture your ammo and use it against you?

Throughout the Cold War, both sides used 7.62mm though.

>> Throughout the Cold War, both sides used 7.62mm though <<

But ours was clearly better, and more likely to work when put into a gun...

Oh, wait... http://www.telegraph.co.uk/news/main.jhtml?xml=/news/2006/12/01/nsoldiers01.xml (penultimate paragraph)

RF

aaaaaaaaaarrrrrrrrrrgggggggggghhhhhhhhhhhh! not all that again!

OK, but during the Napoleonic wars, didn't Britain and France use differen sized musket balls?

Yes. But ours were better.