The present invention provides a pistol with a frame having a rear grip, a trigger facility forward of the grip and an upper surface. An elongated slide is connected to the frame and operable to reciprocate along the upper surface. The frame defines a rear recess open at the upper surface. An insert is included having a major portion removably received in the rear recess and having a frame rail extending from the major portion above the upper surface. The frame rail is adapted to connect with the slide to constrain reciprocation.