[SolitaryMan]

I thought 7.62 = .308 and 5.56 = .223?

[absalom01]

For all practical purposes, yes.  There are some subtle, but important differences, though. (I suspect the '.306' above was simply a typo.)

[xm177e2]

It is .308. Thirty-aught-six refers to ".30 caliber, year 1906," and ".30 caliber" is .308. I think. I'm not super sure, though...

[struwwelpeter]

Lots of different 7.62 - different ones for Kalashnikovs, Dragunovs, and M-14s. Heck, there's even a pistol in 7.62mm.

Discerning the difference takes about, oh, a second or two.

[Sir Francis Dashwood]

I thought 7.62 = .308 and 5.56 = .223?

Me too...