The U.S. Marine Corps is equipping most of their M-16 and M-4 rifles with ACOG (Advanced Combat Optical Gunsight). This device, which does not use batteries, is a well designed scope that provides a red chevron-shaped reticle and bullet drop compensator. For daytime use, a fiber optic system collects available light for brightness and controlled contrast in the scope. At night, the system relies on tritium for illumination. The 4x32 sight allows you to get first round hits at 300 meter, or longer ranges. The sight also allows for better accuracy at closer ranges, with both eyes open. The manufacturer, Trijicon, has been making similar sights for years, and they are popular for police, hunting and military use. SOCOM has long used them, and many marines and soldiers have bought the civilian version of the ACOG with their own money. At a thousand bucks each, ACOG costs more than the rifle its mounted on, and the users consider it well worth the price. 

A Chinese firm manufactures a version of the ACOG sight, but violates the American manufacturers patents to do so. The Chinese version sells for as little as half what the legal version sells for.