cook-off

A "cook-off" is an unintentional firearms discharge caused by an overheated chamber/barrel. When an automatic weapon is fired for a sustained period of time, the barrel will heat up to the "cook-off point", likely to rapidly ignite the propellant of a round still in the chamber. Obviously, this could have unfortunate consequences.

The cook-off point of an M-16/AR-15 rifle, for example, can be reached by rapidly firing approximately 140 rounds in full-auto. The M-16 user's manual states:

"IF A MISFIRE OCCURS IN A HOT WEAPON, REMOVE THE ROUND FAST (WITHIN TEN SECONDS). IF THE ROUND CANNOT BE REMOVED WITHIN TEN SECONDS, REMOVE THE MAGAZINE FROM THE WEAPON, POINT THE WEAPON IN A SAFE DIRECTION AND WAIT FOR 15 MINUTES."

(quote source: www.lepsa.org)

Design modifications to eliminate the danger of cook-off.

Some automatic weapons, like the M249 (FN Minimi) fire from an open bolt. That is to say, the bolt only moves forward and chambers the round after the trigger is pulled. This movement tends to slightly alter the aim-point, so is unsuitable for an individual weapon, but is not such a disadvantage for a belt-fed light support weapon.