A 5.56-millimeter casing is ejected from the weapon

A 5.56-millimeter casing is ejected from the weapon of Maj. John Barbour, Headquarters and Headquarters Company, 56th Infantry Brigade Combat Team, 36th Infantry Division, Multi-National Division – Baghdad, as he looks downrange through his scope while squeezing the trigger of his M4 carbine at Arizola Range on Camp Slayer, Jan. 2. Barbour was zeroing his weapon, which ensures all rounds fired are hitting a target at the aim point.