Although rarely encountered by an average civilian shooter, 12.7x99mm NATO is the military designation for .50 BMG (sometimes designated .50 Browning).

.50 BMG has been in service with the U.S. military since the early 20th century, resulting in multiple different pressure standards developed for this cartridge throughout history:

• US Army .50 BMG Pmax: 54,000 psi (as defined in TM 43-0001-27)
• 12.7x99mm NATO Pmax: 60,481 psi
• .50 Browning CIP Pmax: 3,700 bar (approximately 53,664 psi, roughly equivalent to the US Army standard)

Despite the different standards, virtually all .50 BMG military and civilian firearms today are rated to withstand the NATO pressures. In other words, it is safe to shoot any 12.7mm NATO ammunition in any .50 BMG gun.