Fairly decent footage of a M240B (7.62 mm NATO) medium machine gun firing from the back ramp of a Chinook. A couple times he gets the barrel hot, it should be changed every 500 rounds in this type of environment. When clean and fresh the M240 series will fire 600 rounds per minute, with a sustained ROF of 300 RPM, and barrel swap every two minutes. A proficient gunner can "hot" swap a barrel in about 5 seconds.
http://shock.military.com/Shock/vide...78&ESRC=dod.nl