The gun's original design was as a water-cooled machine gun (see the
M1917 Browning machine gun). When it was decided to try to lighten the gun and make it air-cooled, its design as a
closed bolt weapon created a potentially dangerous situation. If the gun was very hot from prolonged firing, the cartridge ready to be fired could be resting in a red-hot barrel, causing the propellant in the cartridge to heat up to the point that it would ignite and fire the cartridge on its own (a cook-off). With each further shot heating the barrel even more, the gun would continue to fire uncontrollably until the ammunition ran out, since depressing the trigger was not what was causing the gun to fire. Gunners were taught to cock the gun with the palm facing up, so that in the event of a cook-off, their thumb would not be dislocated by the charging handle. Gunners were trained to manage the barrel heat by firing in controlled bursts of three to five rounds, to delay heating. Most other machine gun designs were fired in the same way, even though most featured quick-change barrels and an
open bolt, two features that make air-cooled machine guns capable of sustained fire, and features that the M1919 design lacked.