The Radical Firearms FP10.5-5.56M4-10RPR is a complete AR 15 chambered in 5.56mm NATO. This is a fully Mil-Spec AR-15 pistol with precision machined upper and lower receivers. It starts with a 4140V Chromoly Vanadium Steel M4 Barrel that is Melonite treated for a harder-than chrome finish! The Mil-Spec M-16 BCG is high pressure tested, magnetic particle inspected and melonite finished to ensure flawless performance in the field. It features a free float Radical Firearms 10" RPR (Radical Parallelogram Rail) that is M-LOK compatible and has a full length picatinny top rail.