Abstract: In a firearm of the type having an open-top receiver and a nonrotatable breech bolt longitudinally slidable therein between open and closed positions in which an upper portion of the breech bolt is exposed, the upper portion of the breech bolt is adapted to allow a sighting device to be fixedly but removably mounted thereto. The upper portion of the breech bolt preferably has a pair of longitudinally extending and transversely opposed grooves positioned above but closely adjacent to opposite sides of the receiver. One or more conventional mounting clamps can be employed to securely engage the grooves for mounting a sighting device to the bolt. The sighting device should be sufficiently short to ensure that ejected shell casings do not impact any part of the sighting device.