What are the most common failure modes of the AR15?

[titsonritz]

I've never replaced a firing pin retaining pin, but keep some on hand in case I lose one when cleaning. But, I've never lost one either.

Loss is the main reason to have spare retainer pin, IMO.

[curious1]

Have seen post on sites of broken and bent handles. A spare charging handle in the spare parts. Imagine trying to use the gun without one.

[okie]

Have seen post on sites of broken and bent handles. A spare charging handle in the spare parts. Imagine trying to use the gun without one.

Good point. They stretch over time and will eventually break, though it takes a really long time to happen. What can also happen is the dimensions can be a little off and the carrier will eventually snap them that way. Shouldn't be a problem ever with decent ARs, but could be an issue with shoddy parts cobbled together.

I think the moral of the story of this thread is that a second rifle is the most economical spare parts kit.

[Gatorgrizz27]

A spare BCG is likely to be a “quick fix” if you’re doing some type of training and just want to get back to it rather than diving into diagnostics. I keep most of the common small parts on hand, but I need to stock up on a few more.

I have an issue where my “cheap” parts like mil-spec charging handles, triggers that come in LPK, stack up deep enough to justify building a cheap beater rifle. Then I realize I don’t like cheap crap on my rifles, it gets upgraded, and the spare parts are free once again.

Several of them have taken up residence in a recent 7.62x39 build that I’m treating like it’s an AK though, so they might live there awhile.

[titsonritz]

I think the moral of the story of this thread is that a second rifle is the most economical spare parts kit.

Then you need twice the quantity of spare parts.

[DwayneZ]

If there's no time to diagnose and fix an issue, my spare parts is just grabbing another AR & go.

In more general sense, spare parts should be springs, detents, pins, trigger group, bcg, handle, bolt catch, safety, mag release, castle, buffer, sight(s) of some sort, magazines, maybe a stock, oil. Much of this can be neatly stuffed into a compartment grip and many fwd grips.

Even with all the parts, still need tools to do the work.

[MistWolf]

Any idea what kind of round count on those hammer springs?

And what was the round count on the gas tubes? I've always heard that those will outlast the barrel. Also, what did the gas keys look like? I'm assuming too much gas was escaping and you were getting short stroking?

The first hammer spring was in a brand new AR the owner paid to have assembled for him. Don't know the round count of the second, but it too was an AR the owner paid to have assembled.

The gas tubes had a couple thousand rounds through them. Mine was shot with a suppressor and binary trigger. Second was in an AR owned by someone with access to free ammo. Both gas tubes were from the generic parts bin.

Nothing wrong with either gas key. Yes, short stroking was involved.

[okie]

The first hammer spring was in a brand new AR the owner paid to have assembled for him. Don't know the round count of the second, but it too was an AR the owner paid to have assembled.

The gas tubes had a couple thousand rounds through them. Mine was shot with a suppressor and binary trigger. Second was in an AR owned by someone with access to free ammo. Both gas tubes were from the generic parts bin.

Nothing wrong with either gas key. Yes, short stroking was involved.

So maybe shoddy materials combined with higher than normal heat leading to accelerated wear?

[Combat_Diver]

During my 24 yrs in the Army (all SF) I experienced only one part ever breaking that wasn't my fault. Had a locking lug on my M4A1 bolt break during pre-mission test fire before op (Iraq 06'). Swapped with bolt out of other rifle a M16A2 at the time. My fault was doing a Parachute Landing Fall on my brand new M16A2, smashing its handguards (87'). Since 14' till today been a SOCOM armorer in Afghanistan and Iraq. Number one thing called to fix is a broken bolt. During inspections number 2 is shot out barrels and number 3 is worn gas rings. During rebuild of 10.3" and 14.5" URGs, only thing I prefer to re use is the upper receiver, FH, CH and bolt carrier. New barrel, bolt (complete), gas tube, gas block

Malfunctions on range is usually operator error ie magazine not locking in due to loading 31 rds in a mag or magazine issues. About once a year have a trigger issue not resetting. Cause is a blown primer under disconnector tail. Did have disconnector tail break off once. Have come across two broken ejection port door spring broken (short leg) These guns are all run hard suppressed, unsuppressed, semi and full auto in combat zones. That's about over a thousand guns that I've serviced since 14'.

CD

[Clint]

During my 24 yrs in the Army (all SF) I experienced only one part ever breaking that wasn't my fault.
Had a locking lug on my M4A1 bolt break during pre-mission test fire before op (Iraq 06').
Swapped with bolt out of other rifle a M16A2 at the time.
CD

Sounds like a lot of rounds down range with minimal parts failures, confirming generally excellent durability with the weapon system.

Since 14' till today been a SOCOM armorer in Afghanistan and Iraq.
Number one thing called to fix is a broken bolt.
number 2 is shot out barrels
number 3 is worn gas rings.
CD

Did you notice any general trends in weapon configuration that correlated to increased bolt breakage?
Mk18 vs M4 vs M16?
Suppressor use?

During rebuild of 10.3" and 14.5" URGs, only thing I prefer to re use is the upper receiver, FH, CH and bolt carrier. New barrel, bolt (complete), gas tube, gas block
CD

This is a very practical approach.
The barrel, bolt, gas tube and gas block are wear items with a finite life.
The gas tube and gas block can theoretically last longer, but they're inexpensive enough that they should just be replaced with the barrel to avoid any possible issues.