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.
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.
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.
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.
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 ZedikerPublishing.com and to purchase go to BuyZedikerBooks.com
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.