Trijicon ACOG 5.5x 50mm Rifle Scope - Illuminated Red BDC - The ACOG is an internally-adjustable, compact telescopic sight with a Tritium-illuminated reticle pattern for use in low light or at night. It combines traditional, precise distance marksmanship with close-in aiming speed. This model is designed for use with the M16 family, every feature of its mechanical and optical design was chosen for a single purpose: to provide increased hit potential in all lighting conditions, without failure prone batteries.