Thanks for your help all, I'll get a burris fastfire 3 and see how it fits. I have a local machine shop that can do the work in a day, so sorry Primary Bruce. I just wanted to see or know if anyone put one on without having to mill out the rear sight for a M&P Pro Series 5 inch barrel (not a C.O.R.E.). The answer is harder than I thought. No worries, it will get figured out.
Shoot straight
Shoot often
Shoot safe
Thanks!