There are many different models of the ACOG which are designed to work on AR15's chambered in 5.56. This Trijicon 4x32 ACOG Scope M4A1 Rifle Scope w/ Amber Center Illumination is one of the models designed for AR15's in 5.56. This Trijicon 4x32 ACOG Scope M4A1 Rifle Scope w/ Amber Center Illumination has a BDC reticle calibrated using 62 grain 5.56 ammo out of 16inch barrel.