The “Tap, rack, bang” remedy will clear most stoppages, but it is designed as a way to clear a stoppage, not fix a malfunction or stoppage and keep it from happening again. If you’ve had a repeat of the same stoppage, it’s a good idea to investigate yourself before sending it straight to the gunsmith. You may be able to fix it for free by yourself, and in the worse case, you may be able to tell your gunsmith what exactly is wrong so he doesn’t charge you for diagnostics.
To clarify the difference between stoppages and malfunctions, a stoppage is when the cycle of operation is stopped or interrupted. This can be caused by a malfunction, which is a failure of a part on the gun to operate as advertised, or by any other number of things.
When diagnosing your pistol, it is easiest to start with what part of the cycle of operation it failed.
Most feeding problems are going to be caused by a faulty magazine. Make sure it is properly seated. If you can’t seat it, check the hole for the magazine catch for bends, cracks, burrs or any other obstruction. If you are experiencing double feeds, the feed lips are bent open slightly. In this case, you may also experience the bullet jamming against the edge of the chamber. If the bullet is getting stuck against the feed ramp, the feed lips may be bent inward and not letting the round tilt. If your magazine is not feeding at all, it may just need to be cleaned and lubricated, or there may be a dent in the body obstructing the follower.
If changing magazines is not fixing your failure to feed, check the feed ramp and chamber. If it is damaged or has a burr, the bullet can catch on it and jam instead of smoothly sliding into the chamber.
If your slide will not go all the way into battery on the first round, make sure you are not riding the slide home. If it fails to go into battery on subsequent rounds, the first thing to check is the ammunition. Bulged cases, more commonly seen on reloads, may be too large to fit in the chamber properly, especially if you have a match grade barrel with a tight chamber. Try some fresh, factory ammunition. If the problem persists, inspect the grooves in the slide and the slide rails on the receiver for damage and burrs that might be causing binding. Also check the barrel to make sure it is passing through the front of the slide without binding. It could be slightly bulged, misaligned, or have burrs. One other cause for this type of stoppage is a worn recoil spring. It may not have the energy needed to chamber the round.
Failure to lock will also cause the slide to not go fully into battery. Make sure that the locking lugs and cutouts are clean. Fouling could cause an obstruction of the lugs. If checking all the components involved in the chambering cycle did not remedy the problem, inspect the locking lugs on the barrel, the lug cutouts in the receiver, and any other components involved that your pistol may have. Cracks, burrs, and deformations can all lead to a failure to lock.
Failure to fire is highly dependent on what kind of pistol you are using, and what kind of action it has. Common reasons for this failure include a broken or worn firing pin, a worn firing pin spring, or a worn mainspring. Firing pin wear can be done by pressing in on the firing pin or striker and checking the breech face for protrusion.
If your pistol fails to unlock, the same components need to be checked as in a failure to lock. If you can not pull the slide back at all, try sliding it forward using takedown procedures. If that isn’t possible either, take it to a gunsmith.
Failures to extract can be caused by ammunition, the extractor, or the chamber. Case head separation will tear away the rim, and leave the shell in the chamber. A squib may not give the slide enough rearward energy for the casing to clear the ejection port, and may also leave a round in the barrel. If your ammunition is not the source of the problem, it is most likely the ejector. Check for wear on the hook, or a weak spring. The worst cause of an extracting failure is a pitted chamber. It can cause the case to seal to the chamber, and the best remedy is to replace the barrel. Keep your chamber clean to avoid this.
Ejecting failures are caused by insufficient recoil or a broken ejector. Replace a broken ejector.
Failure to cock will have one of several signs that help with diagnosis. If the hammer rides the slide home, remove it and inspect the notch for wear or built up carbon. Also inspect the sear and sear spring for wear. The hammer may also stay cocked, but fall after the slide goes into battery. This is a dangerous condition and can cause your weapon to fire as if on full auto. The causes are the same as the previous symptom, just with a different result. If your trigger fails to reset, you may have a broken trigger spring, or the trigger and components may be binding due to carbon buildup. On a double action only, the causes remain the same, but instead of the hammer falling or riding the slide home, it simply will not move to the rear, or move to the rear and slip.
Most of these problems are fixed by replacing a faulty part. Many online stores stock the springs and little functional pieces you may need, and most parts are fairly easy to replace. No need to pay a gunsmith unless you don't know what you're doing. Problems with burrs you can file down yourself carefully, but if you are not comfortable with this, or if overfiling may cause an unsafe condition, take it to a gunsmith.