Not all rifles are created equally. This map lists down the various military issue rifles used in different parts of the world. The colors in the maps are meant to represent groups of weapons that come from the same family. Here's a quick look at the listed weapons put together featuring pictures from Wikipedia:

M16

AK-47

AK-74

QBZ-95

Heckler & Koch G36

Of course, each military would probably have more than just one type of gun in their arsenal bunker, but it's still pretty interesting to see the subtle differences in each of the models.

Gizmodo