Originally manufactured by the Unertl Optic Company as a 10x USMC 7.62x51 mm NATO calibrated optic, this scope is one of a limited number converted for the U.S. Marine Corps to .50 BMG calibration for use with M82A1/M107 semi-automatic sniper/anti material rifles. The left side of the adjustment body is marked "USMC" over the serial number "1521", with the original ".30 CAL" marking milled away and replaced with ".50 CAL". As a part of the conversion, the elevation knob was replaced by Unertl with a .50 BMG calibrated knob graduated from 100 to 1,800 yards. Fitted with a pair of "GGG" marked scope rings. Includes a matching numbered Civilian Marksmanship Program (CMP) certificate of authenticity dated January 24, 2019.