the direct impingement gas action is fucking garbage, the m16/ar15 is the only gun ever that uses it, it blows smoke from the cartridge through the gun, fouling the action.
the thought when it was made was that it'd clean out the gun, which is retarded. you have to clean off the goop the powder leaves. it clogs the gun. like when grease gets old and dries up. its nasty.
also it heats up the action.
now arguably the FN FAL is the god of all weapons but it's far more common in asia and south america than it is here; it is fucking EXPENSIVE here.
here is FAL, it uses a full size rifle cartridge, 308 winchester, that can cut right through most body armor.