The .50 Browning Machine Gun (.50 BMG, 12.7×99mm NATO and designated as the 50 Browning by the C.I.P.) is a .50 in (12.7 mm) caliber firearm cartridge developed for the M2 Browning machine gun in the late 1910s, entering official service in 1921. Under STANAG 4383, it is a standard service cartridge for NATO forces as well as many non-NATO countries. The cartridge itself has been made in many variants: multiple generations of regular ball, tracer, armor-piercing (AP), incendiary, and saboted sub-caliber rounds. The rounds intended for machine guns are made into a continuous belt using metallic links.