International Standard Atmosphere
According to JBM Ballistics, using the G7 ballistic coefficient provided by Bryan Litz, the 7.62mm M118 Long Range 7.62×51mm NATO cartridge, when fired at its nominal muzzle velocity of 786 m/s (2,580 ft/s), should have approximately supersonic range under International Standard Atmosphere conditions at sea level (air density ρ = 1.225 kg/m3).