.50 BMG

The .50 Browning Machine Gun is a cartridge developed for the Browning .50 caliber machine gun in the late 1910s, entering official service in 1921. Under STANAG 4383, it is a standard cartridge for NATO forces as well as many non-NATO countries.Wikipedia
 
Bullet diameter.510 in (13.0 mm)
Case length3.91 in (99 mm)
Overall length5.45 in (138 mm)
Used byNATO and many other countries
Rim diameter.804 in (20.4 mm)
Case capacity292.8 gr H2O (18.97 cm3)