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Gun parts break or wear out and stop working. That’s a fact of life — no gun is immune to this, and that includes the AR-15. However, some parts are more likely to fail than others due to the stresses placed on them during firing. Learning what these are can help you identify warning signs and prevent or correct failures.
America’s Rifle: The AR-15
The AR-15 wouldn’t be one of the most popular centerfire rifles in the U.S. if it weren’t reliable and robust. It’s been battle-tested and improved over the course of more than five decades.
Despite its age, it’s the standard for modern tactical rifles. However, even the most well-designed, reliable, and rugged firearms experience parts failures due to improper maintenance, user error, or simple wear and tear.
Learning what parts are most likely to fail in your rifle can prepare you to take the necessary corrective actions. You should also consider keeping an AR-15 parts diagram or exploded drawing in your shop, office, or garage as a guide.
AR-15 Parts Likely to Fail
The AR-15 parts most susceptible to wear and failure are those that experience the most stress during the firing cycle. These include the following:
However, the configuration of the AR-15 bolt locking lugs is asymmetrical because the extractor occupies the position of the eighth lug. This causes asymmetrical stress when firing, which can cause the bolt to crack at high round counts. In addition, the cam pin hole is susceptible to cracking on either side.
If you fire thousands of rounds through your AR-15 rifle due to participation in tactical training courses or competitive shooting matches, you should periodically inspect your bolt for wear around these areas.
Gas tube assembly
The gas tube assembly consists of the gas tube, gas block, and the pins that hold them together. The gas tube is held in the gas block by a retaining roll pin, and the gas block is attached to the barrel by two pins. If these pins break or are lost, the gas tube will become loose, and the seal may become compromised. The gas tube itself can fail, but this is a rare occurrence.
This parts are mostly find on the upper assembly of your rifle, but to give some reference check this article about what a good AR-15 upper assembly should be.
The firing pin is a thin metal rod that strikes the primer to fire the cartridge. Over time, the firing pin can deform, chip, or crack, depending on several factors, including the type of ammunition you’re firing. Hard military surplus primers can wear out firing pins faster. Furthermore, if you’re ever unfortunate enough to experience a pierced primer, the primer is likely to become damaged by the hot gases in the process, necessitating replacement.
The extractor, a beak- or hook-like part that clips over the rim and rests in the extracting groove of the cartridge case, withdraws the spent cartridge from the firing chamber.
At the instant of firing, the pressure in the chamber rises to as much as 62,000 psi (pounds per square inch). Ideally, the bolt will remain rotated and locked long enough for the pressure to drop to a safe level. However, if the action opens too early — e.g., due to being overgassed or having the incorrect buffer installed — the extractor will be subject to additional strain.
If you routinely fire steel-cased ammunition, such as Wolf, this is harder on extractors for two reasons. First, because steel contracts less in the chamber than brass, so extraction can be more difficult. Second, because steel is harder than brass. These two factors, in combination, can accelerate the rate of wear on the extractor, necessitating its periodic replacement.
Your barrel is not likely to “fail” so much as it is to wear out. The lifespan of an AR-15 barrel depends on a variety of variables, from the quality of manufacture, type of material, caliber, and type of rifling. AR-15 barrels chambered in 5.56mm tend to last anywhere between 10,000 and 20,000 rounds. Barrels don’t usually fail in the catastrophic sense. Rather, the rifling and throat are liable to erode from a combination of heat and friction. This can have a detrimental effect on accuracy.
Also called the recoil or buffer spring, the action spring compresses on the rearward stroke of the bolt carrier group and expands to drive it forward, stripping a round from the magazine and feeding it into the chamber.
Springs can lose compression height over time due to heavy use. If you shoot high round counts, you should be aware of this effect and inspect your action spring from time to time, preferably against a new spring for comparison. Springs also wear out faster when used with heavy loads or an overgassed system.
Specifically the bullet-shaped synthetic or rubber tip of the buffer. When the rifle cycles, this tip hits the end of the receiver extension (also known as the buffer tube). This should last a few thousand rounds, but eventually, the rubber part will begin to deform and spread, lessening the shock absorption. This can affect several parts in different ways, including bolt carrier velocity during the cycle.
The purpose of the selector detent is to retain the selector lever in the position you rotated it. If you rotate the selector from “Fire” to “Safe” to “Fire” enough times, this part can become sloppy.
While the magazine is not technically a “part” of the AR-15, it’s essential to the self-loading operation of your rifle. If you don’t have magazines that function reliably, your AR-15 is a single-shot rifle. The D-STANAG or USGI magazine body can deform, the lips can bend, and feeding springs can rust. Stay on top of this and buy quality magazines with stainless-steel feeding springs and anti-tilt followers to avoid some common malfunctions.
The Importance of Maintenance and Spares
Identifying those parts most likely to wear out and break is critical to building your spare parts and supplies kit. Most important, however, is to practice proper maintenance. The AR-15 is a closed system, meaning that foreign matter cannot readily enter the action.
However, the Stoner system also feeds propellant gases into an expansion chamber formed between the bolt and bolt carrier through a tube. This directly contributes to fouling in the action and chamber. As fouling accumulates in the action, it can cause sluggish operation. In addition to cleaning, the AR-15 system needs periodic lubrication.
As a result, it’s essential that you perform proper maintenance on your AR-15 rifle, cleaning and lubricating it often. You should always consult the owner’s manual for your rifle (if you have one) for maintenance and inspection recommendations. An AR-15 parts diagram can also help with the disassembly/reassembly process.
Most likely that you would be doing this more often if you're getting a pre-owned rifle than buying a new one.
The Bottom Line
Some AR-15 parts are more likely to fail than others. Learning what these parts are will enable you to prepare accordingly, keeping your rifle up and running longer.
For more article about AR-15 parts, check out our article about what AR-15 carry handles is really for.