The scenes of John Rambo wasting bad guys with an endless supply of ammunition isn't so unrealistic after all.
While military blog Task and Purpose nailed it with its recent article on what military movies get wrong, the U.S. Army is actually fielding a new backpack that will give soldiers 500 rounds to fire downrange.
The Rapid Equipping Force (REF) has created the IRONMAN backpack, which bring soldiers closer to the infinite ammo Rambo status. It holds 500 rounds of ammo connected to a feeder that attaches directly to the M240B or Mark 48 machine gun. It eliminates the need for an ammunition bearer, although hiking with that much ammo could get pretty rough.
This video explains how the apparatus works, with the firing demonstration beginning at 5:00. Check it out: