Black Hammer isn't the best for everyday sniping. You'll be better with something like Her Benevolence or Praedyths Revenge, but Black Hammer provides the highest potential DPS on bosses for a sniper, and combined with large hitboxes, it can be devastating. True if you miss shots, Black Hammer won't reward you, but it encourages you to land these shots, and on bosses, this is pretty easy. I am not saying BH is or will be the best sniper in the game, I'm saying it'll be a good sniper.