TL;DR: Basically what kris said, but I got interrupted while typing this out and his reply wasn't there when I started
I've been using Black Hammer for a while and I love it, but I can't agree that it's better than Ice Breaker in the majority of situations, let alone 19 out of 20!
Black Hammer is awesome for bosses and higher level enemies that don't like to jump around too much. There's a number of problems with it though:
1) If the enemy you're shooting moves around a lot or likes to hide, it can be very difficult to get 3 precision shots, which very much limits the use of its main perk. It's great for something like a Colossus, but not so great for a Wizard.
2) Not many enemies will survive 1-2 precision shots, meaning the 2nd/3rd shot has to hit one or more enemies to keep the chain going, or you lose the ammo.
3) There's several enemies in the game which don't have critical areas to hit, meaning you either need to use up ammo or switch weapons. e.g. Oracles, Crota Oversoul, Minotaurs etc.
4) The stupid bug that means once you've enabled the Hive damage perk, White Nail no longer works on Hive
All of these issues focus on the White Nail perk and so you could look at it and say that using up ammo isn't the be-all-and-end-all - the stability and damage output also makes Black Hammer a great weapon - but it's definitely the main perk and the major reason to use this weapon over others.
I would go so far as to say that Black Hammer is extremely useful in only 1 out of 5 situations you'll find yourself in, otherwise you'll purposely not use it, even in cases where a high-powered sniper would be of great benefit.
The current Nightfall is a great example of it's usefulness and limitations - destroys the tank, Colossus, and the boss, but difficult on Centurions, and White Nail is all but useless against the Phalanx or their boss variants. Ice Breaker is equally useful in all situations at the expense of (slightly) less damage and sometimes having to wait a few seconds for ammo to regen.