Accidental discharge is the event of a firearm discharging (firing) by means other than a deliberate pull of the trigger, such as dropping a loaded weapon. Accidental discharges (sometimes called ADs by military and police personnel and referred to as negligent discharges several armies) are usually the result of poor maintenance, poor design, defective ammunition or the use of substandard materials in the weapon itself. An assortment of modern handheld firearms using fixed ammunition, including military assault rifles, a sporting shotgun (fourth from bottom), and a tactical shotgun (third from bottom). ... A US Army 45 Colt. ... A negligent discharge(ND) is the Canadian Armys official term for the accidental discharging of a weapon. ... Boxes of ammunition clog a warehouse in Baghdad Ammunition is a generic military term meaning (the assembly of) a projectile and its propellant. ...

Another form of accidental discharge, known as cooking off occurs when a weapon becomes so overheated the firing chamber is hot enough to ignite the propellent charge in the cartridge case, causing the cartridge to fire. This is a particular problem with fully automatic weapons such as machine guns that are fired for long periods of time without allowing the barrel and chamber of the weapon to cool down to safe temperatures. For this reason, modern machine guns are equipped with spare barrels to allow a machine gun crew to replace an overheated barrel with a cool one, thus restoring the weapon to action while the overheated barrel is allowed to cool. Also, majority of machine guns fires from open bolt, so the round is chambered only after pressing the trigger, just before shot. Cooking off is when ammunition is set off prematurely due to heat in the surrounding environment. ... M2 machine gun An automatic firearm is a firearm that will continue to load and fire rounds of ammunition as long as the trigger (or equivalent) is activated or until it runs out of ammunition. ... A machine gun is a fully-automatic firearm that is capable of firing bullets in rapid succession. ... The barrel of a gun or other firearm is the tube, usually metal, through which a controlled explosion is released in order to propel a projectile out of the end at great speed. ... A semi or fully-automatic firearm which is said to fire from an open bolt is one where, when ready to fire, the bolt and working parts are held to the rear. ...

In World War II, the British Sten gun was notorious for accidentally discharging when dropped - the result of an engineering flaw in the trigger mechanism. The Sten gun was a British submachine gun from World War II, notable for its simple design and low cost of production, being made from only 47 different parts. ...