Why Handguns Jam

by Sandy Keathley

To start with, revolvers don’t jam, barring a rare defect in the shell casing size, so let’s move on to semi-automatic pistols. While the semi (or autoloader) is a very reliable device, it is complicated, and depends on several actions working together in harmony. When that harmony is disturbed, the action is subject to several types of intermittent malfunctions, described variously as Failure-to-Eject (FTE), Failure-to-Feed (FTF), stovepipe (see FTE), or just “jam”. These might happen once in 100 rounds, once in 50 rounds, or once or more in every magazine. Failure-to-Eject (which may or may not be a mechanical problem) is often confused with Failure-to-Extract (which usually is). If malfunctions occur more often than once in 10 rounds, suspect something mechanical.

Possible mechanical problems

The extractor hook could be bent or damaged. In that case, you will have major feeding problems. This will require the services of a gunsmith.

It is possible for the forward lips of the magazine to be bent, causing each round to be pointed too low to properly engage the feed ramp. Just look in the ejector port after inserting a loaded magazine. The top round should be pointed slightly upward. You can usually fix that with needle-nose pliers, but a good quality handgun should not have that problem.

If the slide return spring has been replaced with the wrong strength, or has weakened over time, that can throw off the balance of the action. Unless you had previously replaced that spring, there would be no way for you to know if that is a problem, so see a gunsmith.

Barring such mechanical problems, the usual culprits are usually proper fit of the components (cheaper guns), or maintenance (any guns). To understand that, you need to understand what happens
in the cycling process:

  1. The cartridge “explodes” (burns), producing a somewhat predictable force to the rear (not all loads are the same; hotter loads produce more force, but not as much as the next higher caliber). 
  2. The force drives the slide to the rear, impeded only by friction in the rails (grooves), and by a gradually-increasing forward force from the return spring. During this time, the extractor pulls the empty casing from the chamber, ejects it, and clears the magazine, allowing the next round to pop up into place. If the casing sticks a little in the chamber, that also exerts forward force against the slide movement.
  3. The slide continues to the rear until its dissipating force is balanced by the sum of friction in the rails, friction from extracting the casing, and the forward force of the return spring, or it hits the frame (not normal).
  4. As the return spring reasserts itself, the slide is pushed forward again, picks up another round, pushes it to the feed ramp, and up into the chamber. The slide continues “into battery”, sealing the chamber for the next “explosion”.

That is how it should work. That calibration is easily thrown out of balance by increased friction in several places:

  • Extracting the empty casing. 
  • The slide rails
  • Pushing the round up the feed ramp.

Performing proper maintenance can mitigate many of these issues:

  • Some cartridges are coated with lacquer, which, when heated, can leave behind a sticky residue. Using an over-sized brass bore brush chucked into a variable speed drill, polish the chamber with J-B Non-embedding bore cleaner (blue label). Clean the chamber thoroughly with patches and mineral spirits, then with patches and solvent. A shotgun mop attachment is useful.
  • Always clean the rails/grooves with solvent, and lubricate with gun oil (not WD-40).
  • Clean the feed ramp with solvent. If the ramp is not slick, consider polishing it. A small buffing wheel on a Dremel tool is perfect for that. Use a buffing compound made for steel, like White Rouge.

The modern semi-automatic is a complex and sophisticated piece of machinery, but given enough time, it will start to fail intermittently, with results that can be either annoying or fatal. Take care of it, and it will give reliable service for years.

Author: Sandy Keathley

NRA-Certified Firearms Instructor