If you shoot High Power rifle across the course with an AR rifle, the Bob Sled single shot magazine is just the ticket for the two slow fire positions (standing and prone). When using rounds with the longer bullets seated out to an overall length greater than magazine length, some type of single shot follower is necessary. Available in a short length for match rifle shooters and a long length for CMP/NRA Service rifle shooters (approved by the NRA and CMP). The Bob Sled replaces a normal magazine and has a built-in single shot follower designed to accommodate rounds longer than standard magazine length. The Bob Sled locks the bolt into the open position after firing allowing you to load the next round.
Sinclair, Issue:5B, Page:247