Cooking off Cooking off ( or thermally induced firing ) is ammunition exploding prematurely due to heat in the surrounding environment . A fast cook - off is a cook - off caused by fire . A slow cook - off is caused by a sustained thermal event less intense than fire . A cooked - off round may cause a sympathetic detonation of adjacent rounds . Artillery . Inherent design flaws in early 17th century Swedish leather cannon s led to the gun tube overheating which prematurely ignited the gunpowder , injuring the loader . After the cooking off of artillery shell s in the G5 howitzer s in the late 1980s , the South African Army changed commands from " cease fire " to " cease loading " . This allowed crews to fire any loaded shells to prevent them from heating up and exploding . Machine guns . Cooking off is a characteristic of certain air - cooled machine gun s firing from a closed bolt . In such a design , when the trigger is released the weapon feed leaves a final round in the chamber . Residual heat conducts through the cartridge case . If the kindling point of the propellant is eventually reached it will burn even though the primer has not been struck , thus firing the chambered round . Contrary to popular myth , this will not cause the machine gun to " runaway " at cyclic rate of fire ( as compared to a Slamfire ) because each chambered round has to first be brought up to temperature . The time this takes depends on the temperature of the chamber and of the environment , but is usually several seconds , although if caused deliberately may be very fast . During this time the barrel is cooling . Cook offs in machine guns are prevented by : Closed bolt . Most modern infantry assault rifle s fire from a closed bolt , meaning that when ready to fire , there is a round in the chamber of the barrel and the bolt and working parts are in the forward position , closing the breech . Squeezing the trigger releases the striker or hammer , firing the cartridge in the chamber . Assuming proper operation ( no stoppages ) a cook off is possible with this design because a cartridge is kept chambered in the potentially hot chamber , where it can absorb enough heat to cause ignition of its propellant . Caseless ammunition . Caseless ammunition eliminates the metal case that typically holds the primer or igniter and the powder charge ( smokeless powder ) that propels the bullet . The metal case absorbs a large portion of the waste heat of firing . Ejecting this hot , empty case removes that heat from the weapon . With caseless rounds , other means of reducing waste heat are necessary , especially in automatic fire . Tanks . Cooking off is a serious hazard to crews in damaged and disabled tank s . Attempted solutions include storing ammunition under water and insulating ammunition compartments . The current technique , used in tanks like the M1 Abrams , is to armor the compartments and provide blow - off panel s to channel the force of the explosion to the exterior of the tank and prevent the Jack - in - the - box effect . Missiles and air - dropped bombs . The risk of aircraft armament cooking off is a significant hazard during pre - flight operations , especially for aircraft carrier s . Fuel fires , which can spread across the flight deck rapidly and engulf many aircraft , are the most serious risk . This was a significant contributor to the 1967 fire disaster aboard the , when such a fire ( set off by an inadvertently fired Zuni rocket ' s striking the fuel tanks of a waiting A - 4 Skyhawk ) detonated two iron bomb s of Korean War vintage which had been loaded onto the stricken bomber , rupturing the fuel tanks of adjacent aircraft and setting off a chain reaction of similarly cooked off bombs .