When Mr. L. James Sullivan designed a smaller version of Eugene Stoner’s AR-10 rifle to start the AR-15 on its long, infamous life, the M1913 rail (informally referred to as the “Picatinny” rail) did not exist. While firearms designed after 1991 have had the potential of being conceived with the M1913 rail system in mind, the AR-15, like a number of 20th century rifles, had to play catch-up.