One bone I have to pick with our military leaders- they've completely forgotten the whole KISS (Keep It Simple, Stupid) Principle. Dirt will get into EVERY possible crevice, Troops will forget the basics of how to use their equipment in the heat of battle, troops may not have the education need to use complicated hardware , etc.
As Far as rifles are concerned, it's hard to beat the Kalashnikov- rugged, easy to use, no "real" special training required- heck I'd bet you could train a chimp to clean one out, and operate one.