Black hammer is not on the loot table for hard mode.. Yes in Hard mode you get double drops, but that second chance drop at crota will not be black hammer. So to answer your question, if you specifically are trying to get Black Hammer my advice is to find a crota check point on normal. Beat that, and then do all parts of the raid on Hard mode. You will only have 1 drop at Crota for hard however. Hope this helps.