Don't know if this works with Ak's or AUG, but it def works on the M4.

Hello everyone! Just yesterday I found an exploit that can duplicate you ammo. So what you do is take a mag from your gun, make sure the mag can be painted and also make sure the paint you are using is green because black for some reason doesn't work. Put one bullet in the mag and load it into the gun, then put the gun on your back and paint the mag green. It should make the mag disappear from your gun, after that put the gun in your hands and empty it. It should give you one bullet back, but as soon as you get that bullet back just chamber it in the gun. After doing this it should give a full clip of ammo.