Originally Posted by GhostMutt

In firearms and artillery where there is an automatic loading mechanism, a condition can occur in which a live round is at least partially in the firing chamber and capable of being fired, but is not properly secured by the usual mechanism of that particular weapon. The gas pressure produced at the moment of firing can rupture the not fully supported cartridge case and can result in flame and high-pressure gas being vented at the breech of the weapon, potentially creating flying shrapnel and possibly injuring the operator.

"The only stupid question is the one never asked...how else do you learn"...my sensei used to say, probably still does.