First, finish the game.
Second, load the level "the industrial complex" on masochist.
Third, put anything to hold: the left mouse button, any Ctrl or left alt to shoot.
Fourth, start to shoot the "turret" that shoot's fire on you, (the turret take the eternity to explode, maybe it's Indestructible) and be careful by the guys with the shotgun "repeater"
Hope I helped, if you voted down, explain why