M4 For Sale
The elder difference between these models is that the M4 has a "S-1-3" (safe/semi-automatic/3-round burst) trigger battery while the M4A1 defaulter M4 For Sale a "S-1-F" (safe/semi-automatic/fully automatic) trigger group.
Other common accessories include the AN/PEQ-2, Advanced Struggle Optical Gunsight (ACOG), and M68 Aimpoint. EOTech holographic weapon sights are to be part of the SOPMOD II package. Visible and IR (infrared) lights of various manufacturers are also commonly attached using differing mounting methods. As with all versions of the M16, the M4 accepts a blank-firing attachment (BFA).