Diagnosis and Treatment of Common Gun Ailments
by Bob Londrigan,
as published in Front Sight Magazine, March
articles, weíve looked at preventing reliability issues by correcting situations
that can lead to poor reliability. However, sooner or later you are going to
encounter a malfunction for which you cannot find a cause. When this happens,
good diagnostic skills will be crucial to correcting the problem. Whether you
try to analyze the problem yourself or end up explaining it to your gunsmith,
you must understand the nature of problem that is causing the malfunction before
it can be corrected. Also, an incorrect diagnosis may cause you to change the
wrong thing and, thus, make the problem worse. The focus of this article is on
properly diagnosing your gunís reliability issues by using the type of
malfunction as a guide.
Letís first define a standard for reliability. My standard
is that I want to be able to fire at least 5,000 rounds without having any type
of malfunction that I cannot easily explain. This means that if I do have a
malfunction, I want to easily be able to determine its source or root cause. If
it is something I can correct quickly, then I correct it and donít worry about
it. If I canít, then itís time for gun diagnosis and treatment. It is
important to be able to quickly diagnose what is going on because it will enable
you to spend more time practicing and less time working on your gun. Most
malfunctions will be related to either ammo, magazines, or your gun.
Letís begin by examining ammo malfunctions. Ammo
malfunctions include light primer strikes, failure to chamber, and failure to
feed (this could also be a magazine malfunction.)
Light Primer Strike:
Light primer strike can be
caused by high primers, primer flow, or obstructions in the firing pin channel.
Check for high primers by placing a loaded round on a flat surface. You should
not be able to rock the round back and forth. If you can move it at all it
means the primer is high. The primer should actually be seated about 0.003-inch
below the level of the case. If you put a straight edge across the back of the
round, there should be space between it and the primer. To correct high primers,
readjust your loader or use more pressure to seat the primers. Before a match,
check all your rounds for high primers when you chamber check your loads. If
you are still getting light primer hits and you know your primers are not high,
then look for primer flow, trigger/hammer/sear malfunctions, or obstructions in
the firing pin hole (such as pieces of broken firing pin spring or primer
Primer flow is usually caused by excess pressure. Look for a
shiny ring around the outside of the impression made by the firing pin. When a
primer flows it flows into the firing pin hole. As the round is ejected, the
flow is scraped off and ends up in the firing pin hole as a small ring of metal.
This ring will then drag on the firing pin. It can slow down the firing pin
enough to cause light hits on the primer. I have heard many a competitor say
ďbut it is only a little flow.Ē There is no such thing as a ďlittle flow.Ē One
primer that flows may eventually cause a jam. Although it probably wonít, why
take the chance? Readjust your loads or switch powders. Then re-chrono and
check again for flow. Repeat this process until you have a load that makes
major without any flow whatsoever. It also helps to periodically clean your
firing pin hole with a pipe cleaner. This is one of the items I keep in my
range bag just in case. I also have seen situations where altitude or heat
produced enough changes to make a load that was previously fine cause primer
Failure to Chamber:
Failure to chamber can be
caused by many factors such as ammo that fails the chamber check, high primers,
debris caught in the chamber, out of spec brass, a too tight or not properly fit
extractor, or even the overall length (OAL) of a cartridge. When you have a
round that does not chamber completely, set it aside and check it after
practice. At the time it happens, check to make sure there is nothing caught in
the chamber. You might want to strip the gun and look in the chamber. Try
dropping several bullets in the barrel to see if they drop in freely. If they
donít, youíll know thereís an obstruction that needs to be removed.
If a round does not chamber during a match, see if you can
find the round that you ejected during the stage. Later check the round for the
See if it will chamber check.
Make sure it was properly crimped.
Check the OAL to make sure it meets the specs for your load.
Look for high primer.
Make sure the brass is not too long.
If the round fails any of these tests, then you know it was
your fault and not the gunís. You should re-check your loading and case
preparation procedures. If the gun passes all these tests, you need to check
your extractor tension to make sure it is not too tight. If that seems OK, there
is one last thing to check. Make sure the brass is not catching on the firing
pin hole and that there is at least 0.062-inch clearance between the extractor
hook and the breechface. If it passes these checks, then it might be time to
send it to your friendly gunsmith (you do have a gunsmith, right?)
Failure to Feed:
Although failure to feed is usually a magazine problem, you first
want to rule out the ammo. Make sure that none of the rounds in the offending
magazine are too long or have not been crimped. Set the offending magazine
aside and measure all the rounds after practice. If you have ruled out the ammo,
it is most likely the magazine is causing this problem.
Magazine malfunctions can include failure to feed, ejection
problems (every once in a while), and magazines that do not drop free.
Failure to Feed:
If a round fails to feed because it hits the bottom of the feed ramp and stops,
it is almost exclusively caused by the magazine and not the gun. Any round that
hits the bottom of the ramp is likely to cause a stoppage at some point.
Failure to feed stoppages that occur after the round has started to chamber have
other causes and are not usually related to the magazine (we will talk about
this kind of stoppage later.) If you are getting hits on the bottom of your feed
ramp, make sure you have fresh magazine springs and that your followers are
tightly attached to the springs. Inspect the springs for kinks or bends that
were not there before. Measure the outside dimensions of the magazine as well
as the feed lips. Compare these dimensions to a magazine that works well. If
youíre really on top of it, you will have recorded the dimensions of the
magazine when it was working. If you find that something has changed, fix or
replace the magazine and then test again.
Every once in a while I see a magazine cause an ejection
problem. Check the top, front, right corner of the magazine lips (as viewed
from the back). If this point is too high sometimes you will get contact with
the brass that is ejecting. Look for brass marks on the magazine at that
point. Grind a little off the magazine until you no longer get brass marks or
re-adjust your ejection angle higher.
Magazine Not Dropping Freely:
For magazines that do not drop
free, first check to see if this is being caused by the magazine release pushing
the magazine sideways and pinning it in the gun. Hold the magazine release all
the way in and see if the magazine sticks. Then release the magazine button
slowly. If the magazine drops as you are releasing the button, you will need to
trim the inside of the magazine release where it contacts the magazine when the
button is fully depressed. If the gun passes this first test, then squeeze the
grip tightly while simultaneously pushing in the mag release. If the magazine
sticks, then release the squeeze. If the magazine releases as you soften your
grip, then you are close and probably need to change the dimensions of the
magazine only a bit. But if the magazine still sticks, you may have to
substantially change the dimensions. Check to see where the magazine is
binding. Coat the magazine with magic marker and then move it around in the
gun. See if it is sticking front-to-back or side-to-side by checking where the
marker has rubbed off. Then use some careful pressure from the vise to slightly
alter the magazineís dimensions. Measure before and after squeezing, and go
slowly until the magazine starts to drop free. If you have to change the
dimensions too much, it might be better to just buy another tube.
is the issue of gun malfunctions. They include failure to feed, failure to
chamber, stovepipes that hit the port, stovepipes that hit the scope, light
primer hits, gun doubling, hammer falling to halfcock, failure to extract, parts
breakage, lube malfunctions, and weak ejection. As you can see, this topic
requires extensive discussion. Look for it in the next issue of Front Sight