Completely different situational weapons, can't really compare them. Black hammer is good for bosses that have easy to hit crit spots, but if the boss moves often or the crit is small, is worse then other snipers because of the low mag size, while icebreaker is good in most situations, if you are fighting a boss with easy crit spots, it's better to use the black hammer. So pretty much, crit shots go with black hammer, no crit shots, go icebreaker.