The most popular gun in the United States is without a doubt the AR-15. There are millions of these rifles in the hands of everyday citizens and with good reason.
The AR platform is a versatile rifle that is also capable in self-defense situations and for hunting purposes (yes plenty of people us the AR-15 to hunt). Because it is so popular, just about all manufacturers who make these rifles do so to a specification that is known as mil spec.
Because of this and the sheer popularity of this rifle, there is commonality and interchangeability of parts for most rifles, though there are different gas systems, which we’ll touch more on below.
This commonality is great because you can take a lower receiver from someone like Aero Precision and mount it up to an assembled upper from PSA, and have a working rifle.
While they are reliable firearms, they aren’t without their own weaknesses. Anything mechanical will eventually break down or wear out, especially if that thing isn’t taken care of properly.
In other words, AR-15 parts can and do break from time to time. So this begs the question, then:
What are the most common parts to break on an AR-15?
The most common parts that break on an AR-15 are things like the bolt, extractor, firing pin, bolt carrier group (AKA BCG) and associated parts, pins, springs, and of course, magazines.
Most of those are parts that come into direct contact with other metal parts in a reciprocal manner, meaning that they rub on each other causing friction, stress, and eventually breakage or not being functional due to excessive wear.
On the plus side, another great thing about the AR-15 is that all of those parts can be replaced with minimal knowledge, some tools, and a YouTube video.
Why AR-15 Parts Break:
The truth is that any part of your AR-15 can fail at any point, and the best way to ensure that your rifle will always work when needed is to have extra parts so you can fix it when and if it happens.
There really isn’t any specific time frame for any of these parts to break as it will depend largely on each rifle, each part, the owner, and how well they maintain their gear.
There is also the chance that parts could break prematurely based on how they were manufactured, if any mistakes were made during the manufacturing process, material defects, etc.
When we say that parts break, we also include the parts that wear from use, as well. Sometimes you might look at a component that looks fine to your naked eye but is worn out. Other times, parts are visibly broken.
A dead giveaway that you’ve got a problem is when your rifle is doing something specific preventing it from functioning properly, but this isn’t meant to be a diagnostic article. Rather, it’s to take a look at the parts in a general sense.
Let’s take a few moments to discuss some of these parts more in detail.
AR-15 Bolt and Extractor:
The bolt of the AR pattern rifle gets a lot of use. As you’re firing your rifle, the face of the bolt pushes the next round into the chamber to be fired.
The extractor also sits on the side of the bolt and is the part responsible for pulling the spent casing back out of the chamber after being fired.
I was trying to find a diagram to show you, but found this picture on Pinterest that communicates the carrier parts, as well as the bolt itself that is pretty good and uses actual components:
The extractor and bolt are usually one of the first parts to break or wear out just because of what they were intended to do. They’re constantly coming into contact with other metal.
And this is one of the main reasons why a lot of folks will tell you that shooting steel cased ammunition in your AR-15 is likely fine, but only in limited quantities. When you shoot brass cased ammo, the brass is softer than the steel of your bolt face and extractor so it doesn’t really do any damage.
When you shoot steel cased ammo, it’s a lot harder and does more damage or wears the parts out faster.
If either of these parts are suspect, I generally just replace the entire BCG with a new one. I’d rather not take a chance on anything else being damaged.
AR-15 Firing Pin:
The firing pin on your AR-15 is another one of those parts that does a lot. This one, as the name implies, is responsible for setting off the combustion inside the casing that sets the projectile in motion.
In other words, it fires the gun.
There’s more to it than I’m going into here, but suffice to say that when you put the squeeze on your AR-15’s trigger it sends the firing pin forward. The tip of the pin then comes into contact with the primer.
The pin will eventually start to wear down and may break if it wasn’t manufactured to specifications.
Again, if the firing pin ever gets damaged I’d usually just replace the entire bolt carrier group just because I don’t want to play around with something important and take a chance.
AR-15 Bolt Carrier Group:
The bolt carrier group is essentially the main part that holds the firing pin and bolt and helps them operate correctly.
But, it is a little more than that because it houses a few very specific other parts that the gun cannot operate without — like the gas key.
The gas key is the part on the bolt that catches the spent gases, forcing the gas to do its job to cycle the bolt carrier rearward, extracting and ejecting the spent case, pushing the hammer back, allowing the carrier to be pushed forward again by the buffer spring all while resetting the bolt and picking up a new round if available.
Of course that is an overly simplified description, but it’s just meant to be a primer on the topic. Also, not all AR-15s operate exactly this way. The above diagram is for a gas direct impingement system, which is what I’m usually running, but there are others like the piston system that are just different enough that it matters.
The main point is that these parts can break, too. The BCG with the gas key, the cam pin, cotter pin, etc., any of it can break and the best thing is to have an extra BCG on hand so you can keep yourself running.
Of course, the BCG is usually one of the first AR-15 upgrades people make, anyway.
I personally like this one available on PSA’s website that is nickel boron and magnetic particle inspected (MPI) to ensure strength.
AR-15 Pins and Springs:
Pins and springs should hopefully be an obvious group of parts that you should have extra of. There are too many pins and springs to list out, but suffice it to say that any of them can wear out and it’s a good idea to have extras on hand.
A good lower parts kit available from Brownells or a similar retailer will help you on your way and get you back up and running quickly as they have most of the little parts you may end up needing.
The first part to break on just about any magazine-fed firearm is going to be the magazine itself. In fact, I experienced a magazine failure last time I brought my AR15 to the range. The spring isnide the housing of the mag was unable to push the follower and ammo up with sufficient force causing no round to be inserted into the chamber.
It was a really old magazine and I knew it was the reason for the failure right away.
The best practice is to have numerous magazines for your AR. There are several top notch brands out there and you can’t have too many mags.
I strongly recommend Gun Mag Warehouse for any magazine purchases because the small details count. Though someone like Palmetto State Armory will also have a large selection of magazines and if you’re buying other parts from them, adding a mag or two to each purchase is going to be a good idea.
The main point in any of this is to be prepared and ready to keep your gun running if it ever breaks if the SHTF like it may be about to. Having the necessary parts, probably two per rifle, is a good start.