Board Thread:Off Topic/@comment-27144409-20181126150808/@comment-27144409-20190415214712

For starters, not all 7.62 ammo is equal. NATO rifles and LMG's use 7.62X51mm. The classic AK-47 used 7.62X39mm. The AK line has also shifted to include other calibers beyond 7.62X39mm, such as the 5.45X39mm. To further complicate things, the Russians have another 7.62mm cartridge, specifically the 7.62X54mm.

The point is, even if you specify 7.62 ammo, there's still a lot of room for interpertation, even without different ammo types for the same caliber.

X39 is an assault rifle, X51 is a battle rifle

The line is a rather fuzzy one, I'm sad to say.