Hello

Supposedly, as I use my guns, my gun experience should increase. I can fire however much I want, and my XP is still at 0 (i.e. my "ring" is red, instead of yellow). What's wrong?

Ok, seems that I actually do get gun XP, just the meter is faulty. At first it is almost completely transparent, then I get a "nice" yellow triangle, then it again disappers as I level up.

How do you get XP for the other stuff in BR2?

By killing the enemies with environmental hazards - usually impalement. The more you do it in a short time, the more your health and rage bars will increase. I think I've filled both about 2/3rd way through the game.