What are the most common failure modes of the AR15?

[WillBrink]

BCM sells a bolt rebuild kit, basically and extractor and gas rings. I typically keep a spare complete bolt, firing pin, FP retaining pin and cam pin on hand, I figure that covers a lot of ground.

ETA:
https://bravocompanyusa.com/bcm-sopm...e-rebuild-kit/

Thanx. Probably worth just keeping a additional BCG on hand.

[Clint]

This is the way...

Probably worth just keeping a additional BCG on hand.

[rpoL98]

extractor.
primer showing up in the FCG.
firing pin getting damaged from blown-out primer.

[Clint]

These types of failures can occur but are normally very rare in a properly setup AR.


If they do show up in combination, they're generally signs of over pressure and over gassing.

Loose primers are caused by a combination of high chamber pressure and over gassing.

The firing pin damage is from primer piercing, which is caused by a combination of 1) large FP hole in bolt 2)high chamber pressure 3) thin (non-mil-spec) primers

extractor.
primer showing up in the FCG.
firing pin getting damaged from blown-out primer.

[Uni-Vibe]

Lubrication.

I haven't cleaned my main range toy in 1.5 years / thousands of rounds, but she runs without a hiccup wet.

Buddy brought a new in box DPMS out. First round out of the mag, failed to go into battery. He despaired. I inspected. It was dry. Generous CLP anointment and it ran just fine.

[atn729]

Holy crap everybody. Thanks for all the responses. It seems like the general consensus is to keep spares of just about anything related to the BCG. I keep some spare BCGs and rifle so I should be good for now. Again, thanks everyone.

[TomMcC]

Holy crap everybody. Thanks for all the responses. It seems like the general consensus is to keep spares of just about anything related to the BCG. I keep some spare BCGs and rifle so I should be good for now. Again, thanks everyone.

Yep, that's because all the explody stuff is happening at the BCG/barrel extension/chamber interface...that's where things get stressed.

[wanderson]

Spare bolt, maybe a spare extractor as well. Carriers just don’t break but it’s usually just as cheap to buy a complete BCG. I bought a bolt back up kit from AIM Surplus (bolt, cam pin, firing pin & cotter pin) years ago then a year later found a complete Toolcraft BCG on sale for the same price.
In my experience these are the parts most likely to fail with use. An extractor is usually more likely to fail but if your gunsmith skills are minor it’s easier to swap the whole bolt. Swapping a BCG is easier.

Any other firearm I’d say a firing pin too, but I rarely see firing pins break. But they are cheap.

I do recommend keeping spare pins & springs if you gunsmith or build, just because I’ve lost a tiny detent retaining pin or sent a spring flying. But these are parts that don’t see a lot of use/abuse.

Best spare part is another AR.

[blade_68]

I've seen extractor break the tooth off, a few locking lugs on bolt cracked one missing M16a1's. Worn out hammer and disconnecter (s) and carrier key on my first AR "87" vintage (that one went to Will's collection) Cam pin, Gas rings not often, Extractor springs and hammer spring old rifles aka M16a1's. A2s shot out barrel's. Shitty magazines due to AWB some A.D units couldn't even get magazines even not in budget or available.
Just have alot of good magazines, good LPK, gas tube n roll pin and bolt carrier group that would cover 99% of most anything. If more a second rifle. Most problems are lost parts.