The Burris AR-P.E.P.R. Scope Mount was designed with the specific intention of being used on an AR-15. The mount is cantilevered forward an additional two inches. This allows you to mount you scope with the proper amount of eye relief while still allowing the entirety of the base to remain on you flat top upper receiver. This makes for an ideal scope mounting position.
The Burris PEPR mount comes with two sets of scope ring tops. One set ha smooth tops while the other set has Picatinny railing on the top of the rings. This small section of Picatinny railing allows you to mount any number of Picatinny compatible accessories. A popular choice would be to mount a Burris FastFire mini red dot sight on the top mounted Picatinny railing. This will allow you to quickly transition from a higher magnification, primary optic, to a fast action 1x magnification red dot for fast target action.