Out-of-battery
From Gunsopedia
In both firearms and artillery, the term out-of-battery refers to a condition 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. This is a dangerous condition because a round fired out-of-battery can result in pressure being vented at the breech of the weapon, where the operators are. This high pressure venting can rupture the casing of the round and deform the frame of the weapon, potentially creating flying shrapnel.
This article or section is just a stub, and could use more information to fill in the missing bits.
You (yes, you!) can help Gunsopedia and our users by using your own knowledge to expand it