Why does AR-15 which is proven to be reliable suddenly stop working?

[SC-Texas]

I was shooting the WHIDPA 3 Gun match at the Impact Zone on Saturday and my rifle crapped on on the last stage.

I built this rifle to be reliable and it has been through several matches this year including the FB3G (at least the stages I shot) without any issue.

On the last stage it suddenly simply started double feeding. So I shot the largest rifle stage (about 35 rounds) single shot. I was using a C-Products 40rd mag and when the rifle shit itself I changed to the PMAG (Thinking that my proven reliable C-Products 40 had failed me. The PMAG also failed to saolve the proble.

After the match, I did some swapping and confirmed that the mags were not the issue and isolated the issue to the upper.

When I pulled the BCG out, I checked the carrier key. IT WAS LOOSE!

The monkey stake job failed to actually stake the bolts that held the carrier key to the Carrier.

So . . . when your otherwise relaible AR suddenly stops working, check the Carrier key first.

 

[MR Redneck]

OOPS. Did it chew on the upper?

 

[Angered_Kabar]

Great info.

I know LMT stakes their BCGs correctly and they are only $10 more than other popular but non tested and incorrectly staked BCGs.

 

[SC-Texas]

Its so easy to simply blame the mag . . then the lower . . .

 

[jr urbina]

Good advice.

 

[SC-Texas]

Photo of failed stake job!

 

[M. Sage]

Great. Now I'm going to go triple-check the stakes on both of my ARs.

 

[codygjohnson]

Had it happen several times before I learned the proper method of "stakingtheshitoutofthatmotherfucker".people who haven't had it happen just have no idea how bad it can sneak up and screw you at the worst time.

 

[M. Sage]

Had it happen several times before I learned the proper method of "stakingtheshitoutofthatmotherfucker".people who haven't had it happen just have no idea how bad it can sneak up and screw you at the worst time.

You need to write that up with pics so we can put it in the how-to forum. I'd like to learn the right way, too.

Also, folks should be checking their gas keys for loosening every time they remove the bolt group.

 

[ROGER4314]

Wow, that is a totally new on on me. Whenever the AR has feeding problems, chances are good that the magazine is at fault. I have never heard of that happening! Did the gas tube get trashed or was there any other damage? Geeze, you learn something new every day!

Flash

 

[M. Sage]

DPMS and whoever made the bolt that's in my RGuns upper both staked it right. I still might bring a punch home and stake 'em a little more "seriously".

 

[codygjohnson]

Wow, that is a totally new on on me. Whenever the AR has feeding problems, chances are good that the magazine is at fault. I have never heard of that happening! Did the gas tube get trashed or was there any other damage? Geeze, you learn something new every day!

Flash

It just works loose. Doesn't damage anything, but bleeds gas straight into the receiver instead of the carrier. You wouldn't notice anything wrong with it unless you grabbed the key and it wiggled.

 

[ROGER4314]

That's a splendid example of the AR-15/M-16's major flaw......It poops where it eats! Why direct combustion gas at high pressure back into the loading/locking/firing zone? AK's, SKS, M1 Garand, M1A/M-14 and a host of others all avoided this trap by isolating the combustion gas from the business end. Also, the alignment of the tube and the carrier key is critical. I don't know why they work as well as they do. It seems to defy logic.

I just reviewed the military manual and found no check or procedure about the carrier key on the soldier/operator level.

The Complete AR-15 SourceBook shows reassembly of the carrier key and shows two methods of staking the bolts. One method stakes on the sides of the key and the other is in line with the firing pin. Both just cut the bolt head and the carrier key with a punch or a chisel. No torque spec is listed on the carrier key bolts. The book does say that the bolts will shear quickly if they come loose and that suggests that simple retightening is no good. The bolts need to be replaced.

That was a rare event. You just got unlucky.

Flash

 

[SC-Texas]

It is unusal. I disagree with this being a major flaw. Actualy millitary testing has shown that the Pistol guns do not offer a real increase in reliability.

This is why we have no gone to a piston rifle.

This is why SOCOM has cancelled the SCAR-Light project.

A properly staked carrier key will NEVER come loose.

 

[Angered_Kabar]

There's a pretty useful staking jig called the MOACKS. It's a little expensive but if you were going to stake a lot of carriers it could be worth buying it.

I think it does other things than just acting as a jig for staking by the way.

 

[Kyreb]

There's a pretty useful staking jig called the MOACKS. It's a little expensive but if you were going to stake a lot of carriers it could be worth buying it.

I think it does other things than just acting as a jig for staking by the way.

I have been giving serious thought to adding one of these to my toolbox. They are sold by Michigun. The "pocket size" should work fine for a hobbiest such as myself. Still hate to drop $75 on a tool I will use on such an infrequent basis.

Michiguns Ltd. - AR-15 Tools and Accessories

 

[WadeP]

More common than you think; at least they were sorta staked to begin with. I've seen some low-end AR's that weren't factory staked at all.
The MOACKS is a great tool and the only reason that I haven't bought my own is because I have one that I can easily borrow.

Back to the original posting, Sean do you mean it was double feeding two live rounds?

If so, can anyone explain to me why a loose key would cause that? The usual symptom of a loose carrier key is short-stroking and some version of fail to extract or eject and it may or may not pick up a live round.

 

[irishthunder50]

My manual at work so to replace screws if loose, and they need to be torqued to 50-58inch pounds. Also when i stake the key screws i stake them in 3 places. Make sure your not just makeing dimples on the gas key but actually staking the gas key onto the key screws

 

[SC-Texas]

Back to the original posting, Sean do you mean it was double feeding two live rounds?

If so, can anyone explain to me why a loose key would cause that? The usual symptom of a loose carrier key is short-stroking and some version of fail to extract or eject and it may or may not pick up a live round.

No. It was partially extracting the spent case, failing to eject it, and picking up the next round in the mag as the BCG moved forward.

I.E. short Stroking, FTE and then trying to feed the next round. Ending up with a spent case on top of a live round.

 

[Sid]

That's a splendid example of the AR-15/M-16's major flaw......It poops where it eats! Why direct combustion gas at high pressure back into the loading/locking/firing zone? AK's, SKS, M1 Garand, M1A/M-14 and a host of others all avoided this trap by isolating the combustion gas from the business end. Also, the alignment of the tube and the carrier key is critical. I don't know why they work as well as they do. It seems to defy logic.

I just reviewed the military manual and found no check or procedure about the carrier key on the soldier/operator level.

The Complete AR-15 SourceBook shows reassembly of the carrier key and shows two methods of staking the bolts. One method stakes on the sides of the key and the other is in line with the firing pin. Both just cut the bolt head and the carrier key with a punch or a chisel. No torque spec is listed on the carrier key bolts. The book does say that the bolts will shear quickly if they come loose and that suggests that simple retightening is no good. The bolts need to be replaced.

That was a rare event. You just got unlucky.

Flash

The Big M4 Myth: “Fouling caused by the direct impingement gas system makes the M4/M4A1 Carbine unreliable.”

Cleaning Your AR-15 is Pretty Much a Waste of Time | Vuurwapen Blog

A piston AR will have just as much if not more problems due to additional moving parts. A properly staked gas key, like a properly staked castle nut, will hold till the next maintenance schedule and beyond.

Still a good thing to add, checking gas key to the AR's PMCS.