The Schilke 52D is almost identical to the Schilke 52, just a little bit deeper. Curiously, the 52D is much shallower than the Schilke 51D (in fact all mouthpieces of the 51 series are much deeper than their 52 series counterparts... why?).
It is an excellent mouthpiece for the experienced player with a very strong and robust embouchure, although I personally prefer the Schilke 52.