The ASP (Advanced Subsonic Round) was developed to meet the needs of today’s covert special ops teams, providing maximum stealth capability. It is lead-free, frangible, and environmentally safe. When utilizing the 5.56 ASP round with a suppressed M4/M16, the only sound produced is the manual bolt cycling louder than the round fired. The ASP will function with the M4, H&K, and the M16 in semi- and full-auto mode with no modification to the weapon.