It has NOTHING to do with the New Skins. If you have LAUNCH MAN booster on, the Hammer will have 12 bullets when you pick it up....however....once in a while...you will pick up the Hammer, and it will in fact have 16 shells in it....
That is how it looks on the screen when you pick it up....and it does in fact have 16 shells. It just happens randomly once in a while. Ive had it happen to me a few times.
Uncharted 3: 110,000 kills
Uncharted 4: meh