Hey!
So after you exit the elevator on the Tremonius base, there’s is a crashed UNSC ship. Use the grapple hook to swing up there and look for the anti aircraft guns. On one of them, run to the tip of its barrel. There will be a pick up weapon. Pick it up, your hands and hud will be gone. But there will be the scorpion sight. Then you can shoot tank ammo as much as you want, no reloads. Infinite ammo