The standard M24 sniper rifle is chambered for .308 caliber ammunition. This ammunition is also known as the standard NATO 7.62-millimeter by 51-millimeter round. It is one of the most common types of ammunition available.
The M24 was originally designed to fire the slightly smaller .30 caliber round. The U.S. Army had intended to use a special variant of this ammunition designed for greater accuracy and range. On finding that an insufficient number of these rounds were available, the Army switched to the marginally larger .308. A modified version of the rifle, known as the M24A3, uses a .338 magnum caliber cartridge.