A typical stovepipe jam. Click on image to enlarge.
Note that in the above image, an empty cartridge case is stuck in the ejection port at the top of the pistol. This is an example of a stovepipe jam. The reason that this is called a stovepipe jam is because the empty cartridge case resembles the chimney pipe of an old fashioned cooking stove.
A stovepipe jam usually occurs in semi-automatic or fully-automatic firearms and is a failure-to-eject malfunction (i.e.) the cartridge that was just fired did not get ejected from the firearm properly and the cartridge case is partially stuck in the ejection port. This means the weapon cannot load the next cartridge into the chamber properly and will not fire.
There are four major causes of stovepipe jams:
- Limp wristing the weapon: We already studied the subject of limp wristing a month ago. By not holding the firearm strongly enough and not offering enough resistance and rigidity to the recoil forces of the firearm, the firing action may not complete its cycle properly and hence a jam occurs. This is more commonly seen when using pistols.
- Old or bad ammunition: The propellant in the cartridge case may have degraded sufficiently due to age, or the case may not have been filled with enough propellant. Either way, the burning propellant doesn't generate enough power to cycle the action properly and so the cartridge doesn't get fully ejected by the time the slide returns back.
- Bad ejection mechanism: Either the return spring of the slide may be too strong or the ejector spring that ejects the old cartridge is too weak. In either case, the slide moves back and then gets pushed forward and starts to close before the old case is ejected. Therefore, the old case gets caught before it has a chance to fully leave the firearm.
- Spin back: The old cartridge case does get ejected, but it hits something on the way out (e.g. the ammunition belt, or the drum, or the side of the ejection port) that causes it to spin back into the ejection port instead of going out of the weapon. Some rifles are more susceptible to this than others: e.g. the Stoner 63A, which was used by SEALs in Vietnam, occasionally suffered this when configured with a snail-drum magazine which fed from the left hand side. It did not exhibit this issue when configured with a box magazine fed from the right hand side.
Stovepipe jams are relatively easy to clear. We will study how to clear firearms at the end of this series. For now, we will continue studying other types of malfunctions in the following posts.