The CRS 4 x 21 is a high-performance combat rifle telescopic sight designed for 5.56mm (.223) and 7.62mm (.308) weapons.

Two models are available, the CRS-M, with a mount designed specifically for the M16 & M4 series (also AR15 civilian models), and the CRS-P, designed to fit on a Picatinny (MIL STD 1913) rail.

Compact and rugged construction withstands hard use and heavy recoil. The optics are particularly high quality producing an image with exceptional clarityand resolution.The sights feature a range finding reticule and an integral bullet drop compensator (BDC) to allow for allow for trajectory at different ranges.The CRS-M model is specifically designed for use on M16 series weapons, mounting in the carrying handle groove. It is compatible with all M16, M16-A1, M16-A2 and M4 weapons equipment with the carrying handle.The CRS-P model is compatible with any 5.56 mm or 7.62 mm weapon fitted with a Picatinny rail, including "flat top" M4 carbines.Both models can be supplied with a Tritium day/night illuminated