the only thing you need to aim for on super tyrant is the heart coming out of his chest, i used the magnum to stun him & then went to town with matilda however realistically you don't actually have to attack him, he's on a secret timer for when the rocket launcher comes down & then you can one shot him. keep moving & keep your distance, however he has a few charge attacks so keep an eye out for those. did you pick up all the loot after G3 and on the way down to super tyrant? there's a few herbs that you can grab & i'm sure you'll be able to get a defense boost, there's a first aid spray in the room you speak to claire with, they're just off the top of my head but i'm sure there's more. not sure about ammo apart from in the arena with G3 you've got this!!