i was an asshole and went ham on him. I never even let him get to the ceiling holes. I froze/shocked him and unloaded 6 magnum rounds, switched to explosives and let him have it. I think it was like 6 magnums and 3 explosives mixed with shocks/freezes and he was down like a chump. at that point of the game i was only using magnums for bosses so I was good to go. I tried 3/4 times to do it with shotgun and grenades, but just saying

it cuz i was so close to the end. Just make sure to grab as many keys and you shouldn't really have an issue. Same with final double safe heads, just went freeze shock magnum ham.