What are the most common failure modes of the AR15?

[Disciple]

Nobody mentioned gas tube yet.

Is that really a common failure point?

[atn729]

Is that really a common failure point?

I've never had one fail but I want to let more experienced people discuss it

[MikhailBarracuda91]

Is that really a common failure point?

I've never personally had one fail. But I know it's a maintenance item, if you put lots of rounds through a rifle

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[markm]

Gas rings and buffer springs are really the only items I've changed out over the years as a true replacement.

[okie]

So the most common maintenance items are going to be gas rings and extractors. And maybe to a slightly lesser extent, ejectors and main springs.

Then the bolt and the cam pin can both fail without warning. You don't have to worry about it at all with a 20", a 16" you can count on many thousands of rounds, but a 10" is a little bit of a crap shoot, especially depending on what bolt you have.

You should keep an entire spare bolt carrier group. You probably don't need the carrier itself, but gas keys do occasionally come loose, and it's no more expensive to buy an entire BCG than to buy the bolt and all the small parts separately.

Barrels. Again, kind of depends on barrel length and lining. The gas port eroding is the issue with short barrels. You will most likely end up with excessive bolt speeds on a 16" carbine before anything actually breaks or starts keyholling or anything like that. So you'll want to keep some tungsten weights on hand to heavy up your buffer for when that starts to happen, which will extend the life of the barrel for probably another 5-10 thousand rounds.

Now that's chrome lined of course. With stainless or CMV you're going to shoot out the barrel before or around the same time that your gas port is getting to be toast. And of course with 20" barrels gas port erosion just isn't a problem. And it's a lesser problem with 16" mid, but at the expense of some ruggedness in terms of being able to power through the extraction if the chamber gets a little bit dirty. A properly timed carbine with the correct extractor parts is a workhorse in terms of chewing through ammo in less than ideal conditions, like running dirty because of a suppressor, for example.

I'm a big fan of Colt because they are super durable and not much more expensive than the cheapest out there, but of course LMT's enhanced stuff can't be beat, though it is pricy. Like you can get several Colt BCGs for the price of one LMT. And the LMT does still need replacement parts, and you'll be paying 60 dollars each for extractors, which would buy an entire milspec bolt on a good day.

[markm]

The gas port eroding is the issue with short barrels. You will most likely end up with excessive bolt speeds on a 16" carbine before anything actually breaks or starts keyholling or anything like that. So you'll want to keep some tungsten weights on hand to heavy up your buffer for when that starts to happen, which will extend the life of the barrel for probably another 5-10 thousand rounds.

Port erosion happens in the bore. The actual diameter of the port on the outer reaches of the barrel does not open up, and thus the gas flow is still the same or very close to what it originally was.

[okie]

Port erosion happens in the bore. The actual diameter of the port on the outer reaches of the barrel does not open up, and thus the gas flow is still the same or very close to what it originally was.

I don't know where you heard that, but it's inaccurate. It's true that you get more erosion on the inside, but the length of the orifice has as much to do with gas flow as the diameter. That's why gas ports are corrected for size if the diameter of the barrel is changed. The gas cuts into the edge and erodes it like a rivulet in clay soil, resulting in higher flow, in turn resulting in earlier unlocking and higher bolt velocities. The bolt velocity in a carbine (chrome lined) will become an issue before keyholling. ARs that start out with H2s often end up with H3s before the barrel is retired, and the shorter the barrel the more of a certainty that becomes.

[MistWolf]

Parts I've replaced due to wear or failure-
-Extractor spring
-Action spring
-Hammer spring
-Gas tube
-Gas rings
-Bolt catch
-Bolt catch roll pin

A friend replaced a worn barrel

[SonOfAGunn]

It's mainly bolt parts that are wearing for me. Gas rings seem to be showing the most wear since they aren't holding the weight of the carrier anymore. I can't tell that they are worn by looking at them, the just don't hold the weight. The Cam Pins look to be taking a beating as well, but I've never seen one break. There's a visible "seam" or "edge" on the cam pins as well as finish wear.

I've heard that firing pin retaining pins go bad, but I haven't had one break yet. I've got spares of all of these parts, especially the firing pin retaining pins.

[okie]

It's mainly bolt parts that are wearing for me. Gas rings seem to be showing the most wear since they aren't holding the weight of the carrier anymore. I can't tell that they are worn by looking at them, the just don't hold the weight. The Cam Pins look to be taking a beating as well, but I've never seen one break. There's a visible "seam" or "edge" on the cam pins as well as finish wear.

I've heard that firing pin retaining pins go bad, but I haven't had one break yet. I've got spares of all of these parts, especially the firing pin retaining pins.

This is the first I'm hearing of the retaining pins. Would like to get more info on that if anyone can elaborate. Do they just lose their spring from being taken in and out so much, or do they actually break?