MBUS – Magpul Back-Up Sight Front GEN 2, Flat Dark Earth. The new MBUS (Magpul Back-Up Sight) GEN 2 is a color injection molded, folding back-up sight with a smaller profile. 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. A Magpul front sight adjustment tool is included with the purchase of the front sight. Not to be used on an AR15/M16 gas block.