Did another run of JHC, now an Angel of Shotgunnery UV 100% kills one.
The most difficult part of this challenge was actually finishing it with enough bullets to kill the final boss. Shells just stop spawning completely before the last 12 levels and boxes only give you 12 shells every now and then.
This game has a pretty noticeable problem with ammo for some weapons, and I don't think using 3+ levels trying to get Ammo Surplus is a solution to it, seeing how low the amount of ammo dropped by that trait is too.