The radius on the top of an M&P slide is tapered and not flat like on a Glock slide. By the time the CNC mill can cut deep enough to achieve the full rail profile the mill will cut into the plunger safety channel inside the slide and render it not safe to use. There also isn't enough space between the breech face and the rear sight dove to achieve the full cut length for the ACRO footprint. If that wasn't explained to you properly when you first contacted our shop about it we apologize, but that's the reason why.