Armadura/biology

A good way to kill an Armaduras is to aim a shotgun blast at their head. That will usually either stun them so that they need to recover their strength, or instantly reveal the plaga. Instead of taking all of them out one by one, you can expose all of their plagas and then throw a flash grenade, easily killing a boss in six to twelve shots. Be careful doing this, though - when you fight the black ones, they will spawn type-B plagas.

Another good way is to focus at one at a time; blow off their helmets with a shotgun and spray them with the TMP, quickly taking them out. This would be useful for the black Armaduras.