M4/M4A1 Carbine Reliability Issues: Diagnosing the root cause.

M4/M4A1 Carbine Reliability Issues: Diagnosing the root cause.

March 15, 2009

If your Explorer gets a flat does that mean “Fords are unreliable”?
If you put bad fuel in your Tundra does that mean “Toyotas run crappy”?

Stay with me…

When a weapon malfunctions, we often hear “it jammed” or some such non-descript statement that gives us no more information than what we already witnessed–your rifle didn’t fire. To be truly capable of correcting malfunctions and, more importantly, preventing them, the operator must be able to identify which of the five areas are the root cause, and then correct the deficiency. It is very simple and should be taught to every individual issued an AR-15/M16/M4/M4A1-type weapon.

The 5 root causes of malfunctions:…

– Shooter Induced

– Magazine Failure

– Weapon Related

– Operating Environment

– Ammunition

Let’s take a look at these one at a time understanding that some fall under multiple categories. I am not going to cover every possible problem but I want you to understand the methodology so it can be applied to your instruction and training.

Shooter Induced

Failure to properly load is the most common cause of a failure to fire. Some say only load 28 rounds in a 30 round magazine so it is easier to load with the bolt forward. Here’s a tip, load thirty and use proper technique. If you’re doing a magazine exchange to top off your gun then you have enough time to do it properly. Don’t short yourself 2 rounds for a training deficiency.

An improperly loaded magazine is also a common problem. The most common is 31 rounds in a 30 round magazine. This makes it almost impossible to seat in the well. If you do hammer it in, it will do damage to the feed lips (which if repeated will result in feed lip separation and double feeds) and cause the rifle to malfunction on the first shot due to the extreme pressure on the bottom of the bolt carrier by that 31st round. The next problem is one I have witnessed many times in HK steel magazines (and magazines of similar dimension) that have a wider spine than the standard aluminum GI magazines [a.k.a. USGI magazines]. When using a stripper clip and standard GI stripper clip guide a case can get stuck in the spine and bind the magazine. *This is of critical importance to military personnel for the following reason. If you get a resupply and those steel magazines are present, who loaded them? They were probably loaded by someone who was tasked to “load 100 magazines as fast as you can?” With that you won’t know that your magazine is not serviceable until your rifle doesn’t fire when you need it to do so.

Shooter induced failure to feed or double feed happens in several ways. When an operator loads with the bolt forward on an empty chamber and then manually cycles the bolt but doesn’t pull it all the way to the rear or allow it to go forward under its own spring tension often a malfunction is induced. A bolt over base malfunction is caused when the bolt is not pulled back far enough to clear the top round in the magazine (short cycling) and the bottom lug catches the case about 1” from the base and pins it in the feedway. A shooter induced double feed is caused when the bolt is ridden forward so it rests on the base of the case in the chamber but does not have enough force to snap the extractor around the rim (failure to lock). When the hammer falls and the weapon does not fire SPORTS (Slap-Pull-Observe-Release-Shoot) or tap-rack will cause a double feed. Another version of that is when clearing a stove pipe improperly (using SPORTS instead of pulling the case out manually).

The last is far too common and stems from a lack of understanding. This is when the operator puts a magazine in the well with the bolt locked to the rear and then slaps it hard enough to dislodge a round from the feed lips. When the bolt is released it causes a double feed. The only time and the only reason you slap the bottom of an M4 magazine is when loading a rifle in the bolt forward configuration or conducting SPORTS. The operator is slapping the base of the magazine to overcome the tension of the compressed spring as transmitted through the top round against the bottom of the bolt carrier. When conducting SPORTS it can break loose a follower that may be jammed. Slapping the magazine with the bolt rearward is prone to cause a malfunction and at best unnecessary.

Magazine Failure

Failure to feed is most commonly caused by a weak spring. If a relatively clean magazine fails to feed then the spring is fatigued and the magazine is not serviceable.

Double feeds are caused by feed lip separation. When the feed lips are wider than the factory spec (use a new magazine to compare to your old ones) then it is unserviceable and can cause the worst type of malfunction you will encounter: the bolt-override double feed. If a magazine double feeds once, it will do it again. They don’t get better so get rid of them. *(If a magazine is repeatedly loaded with 31 rounds and forced into the well, it will not only cause a malfunction of the rifle but will also force the feed lips wider because the rounds cannot go down, and they will damage the magazine. I have witnessed an operator split the spine on two polymer magazines when loaded with 31rds.) This is a magazine failure caused by the shooter using improper technique, and thereby causing damage.

Failure to drop free from the magazine well is a sign that the feed lips are separating and the magazine is borderline unserviceable, or the magazine is manufactured out of specifications. Regardless of reason, all magazines should drop free when empty. If they will not, replace them.

Weapon Related

Broken parts happen to any machine, and if you read the previous article on M4 reliability, you’ll see that weapon-related malfunctions are relatively uncommon if you conduct proper maintenance.

A serviceable failure is when an otherwise fully functioning, properly maintained weapon, magazine and ammunition fail to function. This can happen but it is extraordinarily uncommon. I can’t remember when I had or witnessed a malfunction for no apparent reason…but I guess it could happen since no machine can be expected to work perfectly, 100% of the time.

Operating Environment

Sand, salt, cold and humid environments can wreak havoc on any machine, so the weapons-maintenance schedule must be modified, and PM (Preventative Maintenance) performed more frequently. Sandy environments do require lubrication, but only on the friction-related areas, so as not to attract excessive dust. Cold environments require a low-viscosity, cold-weather lubricant, and humid and salt environments necessitate a lot of lubricant to help resist corrosion. You can minimize the effects of your operating environment by modifying and adapting your maintenance protocols.

Ammunition Related

Duds, i.e. improperly manufactured or environmentally compromised ammunition, do occur, but they’re rare if simple steps are taken. Proper storage at ASP/AHA (Ammunition Supply Point/Ammunition Holding Area), along with rotation of operational ammunition, can dramatically reduce the likelihood of ammunition-related failures. *Be aware that .223 Remington and 5.56x45mm NATO are dimensionally different. 5.56 often use longer, heavier bullets and this necessitates a lengthening of the throat, lead and free bore in the 5.56 mm chamber. While .223 Remington can be fired in a 5.56 mm chambered guns without issue, firing 5.56 mm ammunition in a .223 Remington chamber can produce excessive pressure even above the 5.56 mm specifications due to the shorter throat, lead and free bore present in military chambers. Know what your rifle is chambered for!

In order to solve a problem, you must know its source. Breaking malfunctions down into the above five root cause categories, or combination of these categories, will simplify this task. With this template, one can remedy a problem simply, rapidly and effectively, and help prevent it from happening again. Although there are many more problems under each heading, for the purpose of brevity, I did not try to include them all. The goal here was to present a logical framework on which to base your solutions, and guide your training and pre-operational weapons checks. Know your tools and master them. Remember, a gunfight is a gunfight, no matter who signs your checks–or what you’re wearing!


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