Magpul Industries MBUS Back-Up Front Sight Gen 2, Fits Picatinny Rails, Flip Up, Flat Dark Earth MAG247-FDE The MBUS (Magpul Back-Up Sight) is a low-cost" color injection molded" folding back-up sight. The MBUS Front Sight is adjustable for elevation and fits most 1913 Picatinny-railed hand guards" but is specifically tailored to the AR15/M16 platform.