MALFUNCTIONS: UNDERSTANDING HOW TO DESCRIBE A "JAM"

The more I hear it, the more it hurts my ears. 

"It was shooting fine. Then it started jamming."

"Every other round, it jams."

"After I fire the first round, it jams."

"When I release the slide/bolt, it jams."

A "jam" is a very general term for a malfunction. Usually, when someone is describing a problem with how their firearm is functioning, they will use the term "jam," after which I quickly interupt them with a request for clarification to help me narrow down the possible sources of the problem.

There are 4 general categories of malfunctions:

FAILURE TO FIRE - the hammer falls, but the firearm fails to ignite the primer in the cartridge and fire the bullet. Usually a problem with either the firing pin, too much headspace, or bad ammunition. THIS IS IMPORTANT: If you hear a "pop", but the gun did not fire, there could be a 

FAILURE TO EXTRACT - after firing, the firearm fails to pull the fired cartridge case from the chamber. Often a poorly fitted or broken extractor, a dirty chamber, or a malformed or improperly sized cartridge case. In semi-auto rifles and shotguns, a gas system problem can cause extraction issues as well. Reloads that have been reshaped multiple times can cause the case have been known to lose the ability to rebound after the pressure of firing expands the case, causing it to get stuck in the chamber.

FAILURE TO EJECT - the firearm fails to fling an extracted case out of the receiver. Can be caused by a broken or missing ejector, or a poorly fitted extractor that does not hold the case against the breech face of the bolt long enough for it to strike the ejector properly. In semi-auto rifles and shotguns, a gas system problem can also cause this malfunction.

FAILURE TO FEED - when closing a bolt on a rifle or shotgun, or releasing a slide on a pistol, either the next round in the magazine is completely missed, is pushed only partially out of the magazine, or binds and gets stuck before being pushed all the way into the chamber. This malfunction has a few more causes originating from many possible sources, and can be more difficult to pin down.  Sometimes this is a problem with the magazine - bend or misaligned lips of the magazine, with where the magazine sits in relation to the bolt face and/or the feed ramp, how the follower positions the round, or a follower spring that applies too much or too little pressure. There could also be machine marks or burs on the feed ramp or around the entrance to the chamber or on the breech face or on the extractor that snag the brass case. A poorly fitted extractor can also prevent a round from feeding properly. In older firearms, modern ammunition dimensions may not be as close to those of the ammunition the firearm was designed to fire. A common example is older 1911A1 pistols and jacketed hollow point (JHP) ammunition. When John Browning designed the 1911 pistol, it was for military use with the 45 ACP full metal jacket (FMJ) round, before JHP was ever developed. Many of the 1911's manufactured today, use the same design and can have problems feeding JHP ammunition reliably.

So if you experience a malfunction with a firearm, consider whether you are experiencing a Failure to Fire, a Failure to Extract, a Failure to Eject, or a Failure to Feed. It will make describing the problem to your Gunsmith or warranty repair facility much more efficient, and it will increase your own knowledge of how your firearm functions.