Mulligan is a throwaway perk. White Nail is the whole of the weapon. Previously, that was fine because the reward for succeeding with White Nail was so good. If they are taking that away, they should change the other perk to one that actually synergies with White Nail. That way the weapon can still be good without the infinite ammo problem. Frankly, though, were I a developer wouldn't nerf Black Hammer or Gjallarhorn at all. I would leave them as a test for whether an encounter had been well designed. If someone can gain a significant advantage by using either of those weapons, then the encounter is too reliant on the boss being a bullet sponge, and its time to rework it with better mechanics.