ACOG is a composite material that has a magnification of 2.5x and a focal length of 16mm.
ACOG is an abbreviation for Air Combat Optical Gunsight, which was introduced by the military in 1979 as a telescopic sight for fighter planes. The actual optics originally used were from the Model A scope series but improvements have been made over time to make it better suited to ground work as well as aerial applications. In 1985, this scope was offered commercially and it's been popular ever since with both law enforcement personnel and civilian shooters seeking accuracy at long ranges.