Cooking off

"Cooking off" is also a technique used when throwing grenades to achieve a controlled, predictable explosion.

Cooking off (or thermally induced firing) refers to ammunition exploding prematurely due to heat in the surrounding environment.

Artillery

Inherent design flaws in early 17th century Swedish leather cannons led to the gun tube becoming deformed which prematurely ignited the gunpowder, irretrievably spoiling the loader's otherwise good day.

After the cooking off of artillery shells in the G-5 field gun 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.

Rifles

Cooking off is a characteristic of certain machine guns, especially those firing from a closed bolt, that are air-cooled, and capable of sustained use. When the trigger is released, the weapon feed leaves a final round in the chamber, where heat ignites the propellant firing the round, which will then cause the weapon to reload and fire again, this will continue until all the weapon's ammunition is consumed. Cooking off limits the rate of fire of many rifles, since heavy use will heat up the gun's barrel.

In the case of the US M249 or some other squad assault weapons sustained fire of only a few hundred rounds per minute can create sufficient heat. Inefficient or insufficient cooling of the barrel or chamber can cause either a cook off or stoppage of the gun through metal expansion. For rifles with very light barrels, such as the M16, the long term sustained rate of fire is as low as 16 rounds per minute, owing to limited heat dissipation and the risk cook-off.

Caseless ammunition

Caseless ammunition eliminates the metal case that typically holds the primer or igniter and the explosive charge ("gunpowder") 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 tanks. 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 panels to channel the force of the explosion to the exterior of the tank.

Missiles and Air-Dropped Bombs

The risk of aircraft armament cooking off is a significant hazard during pre-flight operations, especially for aircraft carriers. Fuel fires, which can spread across the flight deck rapidly and engulf entire aircraft, are the most serious risk. This was a significant contributor to the 1967 fire disaster aboard the USS Forrestal, when such a fire (set off by a misfired Zuni missile striking the fuel tanks of a waiting A-4 Skyhawk) detonated two iron bombs of World War II 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.