Modified M16A2 5.56mm rifle used by US Marine, Iraq, 2004 period.

From Getty:

BAGHDAD, IRAQ - MAY 19: U.S. Army 1st Cavalry Sergeant Shawn Evenson, from Raleigh, NC stands guard near the media positions outside the convention centre on May 19, 2004 for the court-martial hearing for Specialist Jeremy C. Sivits, in Baghdad, Iraq. Sivits was given the maximum penalty (one year incarceration, a reduction in rank, and a loss of pay) for his role in the ongoing Iraqi prisoner abuse scandal at the Abu Ghraib prisoner detention facility located near Baghdad. (Photo by Scott Nelson/Getty Images)