How do you kill the heavy gunner guys with an SMG? I can only do it with tactically placed barrel explosions so far, but do they have a weak spot?
Just guessing but the 50 cal,maybe? I use grenades for the armored guys,but I'm not that far into the game yet.
I believe we get armour-piercing ammo later on.

I'll have to give it another go with the heavy attack later.