This is a future US Army replacement for the M16/M4 series of weapons. I designed it based on the rejected XM8 and the Israeli Tavor bullpup of the IDF. It fires a larger caliber than the OTL weapons, the 6.8mm round. Rail systems on the rifle allow for the mounting of different equipment.
The bottom M8 has a fictional Metal Storm stacked grenade launcher. I based it slightly on the 3GL offered by Metal Storm, it's not a underslung weapon. My 3G has three caseless grenades stacked one behind the other. It's a very light rifle made with composites.