Six Troubleshooting Solutions for AR-15 Function

By Glen Zediker published on in Firearms, How To

When something goes wrong and the rifle won’t fire, the first question should always be, “What changed?” Before answering that, we have to determine—or at least I determine—whether we’re talking about a “fresh” rifle going through its shakedown period, or a (previously) trusted gun that’s suddenly decided to stop running. If it’s the first scenario, there’s a longer list of possibilities that include original parts, conditions, and installation quality. This article will focus on the previously-functioning rifle that’s taken a vacation from operation.

carrier key screws top, staked carrier screws bottom

Top:Here’s a new carrier sans stakes. There was no adhesive on this one either.
Bottom: Here’s the same carrier after stakes.

If an AR-15 that was working fine starts having problems (and these problems are exclusively failures to cycle correctly: fire, eject, feed), the “first question” becomes: What changed?


For reasons ranging from clear to cloudy, not all loads function the same in all guns. If you’re a handloader, double-check cartridge dimensions to ensure nothing changed with your dies, and certainly recheck the charge settings, etc. This is a reason to keep loaded samples cataloged and handy for reference.


A short stroke happens when the bolt carrier doesn’t get far enough to the rear to pick up a cartridge from the magazine and chamber the next round. Therefore, the bolt does not lock back because the bolt stop couldn’t engage. The cause for this is either not enough oomph! from the gas system (a leak) or too much friction or resistance in operation (grit and grime).

First, check the bolt carrier key. One of the often overlooked—and more common—causes for abated gas action is a loose key. If the key is loose, that will be your leak. however, if installed correctly, it should not come loose. Should not. Installed incorrectly, it probably will come loose, and I’ve seen many that were incorrectly installed.

Mark Brown Carrier Scraper and bolt carrier group for an AR-15 rifle

This is a Mark Brown Carrier Scraper. A few turns each cleaning will prevent carbon build-up from ruining your fun. The volume of grunge that emerges from the use of this tool will amaze.

The key is held fast by two screws. Most specs I’ve seen call for 30 to 40 inch-pounds of torque, and I say that’s not enough. They need to be tighter than that. Most of the better builders I know don’t use a torque wrench for this operation.

The trick is to ensure these screws are staked in place. There seems to be an increasing number of carrier key screws installed using thread-locker (or not) in lieu of staking. If this is (truly) correctly done, it’s okay. However, it’s often done incorrectly. Some strongly disagree with the need to stake screws, but it’s a certain cure.

Staking is best done using a specialty tool but can be effectively done with a prick punch and hammer. It’s not always going to be a pretty job using hand tools, but as long as some metal is displaced inward, from the key to the screws, to secure the screw heads from rotating, it will be functional—that’s why the screw heads are knurled, by the way.

Bolt Carrier Carbon

The area inside the bolt carrier where the tail end of the bolt goes can get caked with carbon. That fouling is tough enough to warrant removal, and it’s the source of many malfunctions; the bolt gets sticky. Given that this area is likely neglected, eventual build-up will happen.

AR-15 gas manifold

A gas manifold should be seated fully flush and securely against the barrel. Loctite “blue” on the set screws is a good idea but I don’t like the risk of gluing the manifold to the barrel. Glue and gas ports are not compatible.

There’s a specialty scraping tool I prefer but GM Top Engine Cleaner (get it at the parts counter at a Chevy dealer) and some brushing can dissolve the majority of caked carbon. Seafoam and Chevron Techron cleaners can substitute. Routine rifle bore solvent may be inadequate to achieve the desired result.

Gas Manifold Leak

Another leaky spot can be around the gas manifold or block (where the gas tube fits into on the barrel), especially when there’s an aftermarket gas block installed. Fit issues are common enough when there are incongruences between the block’s inside diameter and the corresponding barrel area exterior dimension. It doesn’t take much gap to provide an outlet under that sort of pressure. You can usually see the blow-by firing the rifle from the hip, also look for streaks.

About all that can be done here is to make sure the screws that retain the block in place are tight. No glue! There’s a big risk of the thread-locker getting into the gas port. That’s a sure way to cap the flow. Misalignment between the gas port in the barrel and the corresponding inlet in the block can easily cause abated flow, but most blocks have sufficiently oversized inlet holes that perfection isn’t nearly necessary.

AR-15 rifle extractor

If it’s a failure to eject a spent case, do a quick check of extractor and ejector condition. An extractor spring or ejector spring might be broken. These springs, by the way, often break rather than sack and weaken. Breakage is common in full-autos (heat-induced).

Dirty Chamber

Last, and decidedly not least, is to keep the whole daggone thing clean, and that includes the barrel chamber! This area is often neglected in rifles that have otherwise meticulously-maintained barrel bores. Thread a .357-caliber pistol brush on a short rod and scrub it each barrel cleaning. Keep the bolt body lubed and keep changing the oil: Lube it, shoot it, clean it—lube it, shoot it, clean it. Rinse and repeat.

Residual grit is especially an issue with a suppressor-equipped gun (gets into the magazines too). Perhaps, unlike a few other firearms, my experience has been that lubing the fool out of an AR-15 helps to keep it from collecting residue.

Do you have tip for maintaining or troubleshooting AR-15s? Share your answers in the comment section.


The preceding is a specially-adapted excerpt from the book The Competitive AR-15: Builders Guide by Glen Zediker and Zediker Publishing. For more information visit and to purchase go to

About the Author

Glen Zediker has worked professionally with some of the greatest shooters on the planet, as well as leading industry “insider” rifle builders, manufacturers, and proven authorities on gunsmithing, barrelmaking, parts design and manufacture, and handloading. And he does pretty well on his own: Glen is a card-carrying NRA High Master and earned that classification in NRA High Power Rifle using an AR-15 Service Rifle.

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Comments (8)

  • Phil Auten


    Thanks, great article! Being new ti AR’s I really needed this info, not immediately, but I’m sure in the future.
    BTW, the WD in WD-40 stands for “water displacer” and it is most definitely NOT a lubricant.

    Phil in TX


    • OldGringo


      LOL. Read my comment again, slowly. My comment was I prefer WD 40 or silicone, which I said, is better than any lubricant, but then I followed it up with any lube will do (if you do not want WD 40 or silicone). Guess I need much longer explanations?


  • Rick


    If the front sight base, (especially with low profile after market style) is not properly secured it has a tendency to creep forward just as a scope does. This will result in loss of gas pressure to the bolt.


  • OldGringo


    Run the guns wet. WD 40 or silicone is better than lube, but any lube will work. Second, if you have a 223 chamber or match chamber or have sticking cases, get the little flex hones. They will give you a mirror chamber in 3 minutes.


    • Day0ne


      WD-40 is not a lube, it’s a solvent


    • OldGringo


      Read my comment again slowly, I said recommend Wd 40 or slilicone, which is better than any lube…..but any lube will work.


    • wolf ryet


      If you read the cans instruction label it can be used as a light lube. Further more many lubes will work as solvents. I use light lubes all the time to clean grease off of wiring and extension cables and car parts. In addition many lubes have warnings about compatability with hydrocarbon compounds and plastics.


  • 70's Ops


    Well, this was an issue I confronted when building my SBR and Grendel. Knowing the regimen I used in the military made me research things quite well. My answer….Anderson RF-85 parts. Honestly they’re damn near dishwasher safe. Nothing sticks to them. No lube to buy. No lube to catch and hold carbon deposits. A thorough swabbing with a little bottle mop dipped in dawn and water. A quick rinse and blow dry with an airhose, and tah dahhh. Ready for next time. It really is almost unbelievable. But, 300 – 400 rounds between cleanings is acceptable. Then the above procedure and its sparkling clean. If you haven’t already, check it out. You’ll be amazed.


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