AR-15 Issues… You Never Know What’s Going to Walk Through the Door

SiersBy John Siers a.k.a. “Gunsmith Jack”

As a gunsmith, I have to love the AR-15 just because of all the business it brings me. Probably a third of the customers that walk through my door are bringing me an AR with some silly problem or other. Of course, there are a lot of ARs out there, and a lot of unqualified people trying to assemble and/or “customize” them. That’s a little scary, but so far most everything I’ve seen has been a “fail safe” problem – in other words, no shooters were injured in any of the incidents described here.

The most dangerous issue I came across involved a customer who assembled his own lower receiver and failed to make sure the secondary sear could move freely. It had a tendency to stick in the disengaged position, giving him an unreliable (and illegal) full-auto rifle. He brought it to me after being booted off his local shooting range for violating their prohibition on full-auto fire. I solved his problem with a little fitting and polishing to get it working properly.

Most of the issues I see are less dangerous, like the customer who brought me two AR uppers. One was a traditional .223 / 5.56, while the other was a .300 Blackout. Both had the same issue: they simply would not cycle… at all. No eject, no feed, no movement of the bolt carrier when fired. They could be cycled just fine with the charging handle, but did nothing at all when fired except wait to be manually cycled. In short, they were behaving like bolt-action rifles.


Isn’t that hole in the gas tube supposed to be on the BOTTOM?

OK… obviously a gas system problem and when I pulled the front end apart, this is what I found (see picture). Now, what could possibly be wrong here? Hmmm… isn’t that hole in the gas tube supposed to be on the BOTTOM?

Both of the uppers had the same problem – an upside-down gas tube – and in fairness it was not the customer’s fault. He had built his own lower, but had purchased both uppers completely assembled with barrel and handguard from a well-known internet vendor.

On the other hand, some problems are definitely caused by user error. One customer tried to replace the A2 sight-ramp gas block on his rifle with a quad rail block. No problem – just knock out those two pins on the bottom, unpin the gas tube, and it should slide right off. Unfortunately, nobody told him those two pins on the bottom were tapered and he managed to drive them about halfway out in the wrong direction before he figured out they wouldn’t come out that way. Then, of course, he bent them while trying to drive them back in. At that point he brought it to me. I had to cut off the pins, then drive them back out. Original gas block was pretty much ruined, but the barrel was OK, so I was able to install his new gas block without a problem. The good news about the AR platform is that just about everything is fixable / replaceable with a minimum of fuss, as long as the lower receiver shell isn’t damaged or defective.

But what if it is? I recently ran across a problem that’s probably not very common, and I had to come up with an uncommon solution. The gun was a cobbled-together mess that matched a brand-name lower (clearly marked .223 / 5.56 caliber) with a no-brand upper and a 7.62×39 barrel (first time I’d worked on an AR that speaks Russian). That’s OK, as long as the bolt, magazine, and buffer are suitable for the cartridge (which they were).

The customer hadn’t built this one – he’d traded an old flat-bed utility trailer for it, but after his first trip to the range he was beginning to think the other guy got the better of the deal. He got a whole bunch of misfires and failures-to-feed – not jams, bolt just didn’t pick up the next round from the magazine, giving him a resounding “click” as he pulled the trigger on an empty chamber.

The first suspect was the cheap, steel-cased Russian ammo he was shooting (the trailer deal included about 300 rounds of it). I looked at some of his misfires and saw light firing pin impressions on primers that were obviously set too deep in the case. Mil-Spec for .223 calls for primers to be no more than .008” below flush, and these were running as much as .015” – probably not a problem for an AK-47, which has more firing pin protrusion than an AR. I also noticed that the junk ammo wasn’t feeding smoothly in the magazine (though it was marked as being for 7.62×39). This is going to be an easy fix, I thought, and I took the gun to the range with some good-quality Fiocchi ammo, brass-cased and properly primed stuff that I use with my own AK-47.

Turns out I was half right. The misfires disappeared with the good ammo, but the missed feeds did not. OK… back to the shop. A look at the magazine showed the quality ammo was feeding properly when stripped off by hand. No problem there. The magazine was a very tight fit in the mag well, but when shoved all the way in it would feed and chamber the round just fine. The problem seemed to be just a little bit of play in the magazine catch, that would allow the magazine to move downward just a little bit after a round or two was fired. Spring tension pushing the rounds upward against the bottom of the bolt would tend to push the magazine down, but because it was such a tight fit that wouldn’t happen until several rounds were fired… and then the bolt would miss picking up the next round. The first suspect was the magazine itself, but that wasn’t the problem. The slot in the magazine was properly cut and positioned.

Nor was the magazine catch itself the real culprit. The first photo below shows the stock catch installed in a typical lower receiver shell. This is the way things are supposed to look, as I’m sure most of you have seen many times. It’s a nice snug fit, with just enough clearance to let it slide straight out to release the magazine.

The way it should look.

The way it should look.

The next picture shows the magazine catch installed in the customer’s gun, and now the problem is obvious. The slot in the lower receiver shell is cut too wide – not by much, just maybe a sixteenth of an inch or so – enough to let the catch pivot downward, allowing magazine to drop just enough that the bolt will miss picking up the next round.

NOT like this!

NOT like this!

This was a factory defect. When I pulled the mag catch out and looked at the slot, I could see faint marks in the bottom where it appeared the tool had slipped a bit. The top part of the slot was cut correctly and the hole was properly positioned, but then some extra metal got taken off the bottom.

So, what do we do about this? I can almost hear Bob saying “you just need to TIG weld a little bit of metal on the bottom of the slot, then re-cut it to the proper dimension….” Unfortunately, my skill at TIG welding aluminum rates poor to zero, and I don’t have the equipment to properly mill out that slot again. I need a better solution than that. Of course, I could just tell the customer he needs a new lower receiver… “and fortunately, I have one in stock. Now, just fill out this Form 4473 because according to ATF I am actually selling you a new gun.”

No… I came up with a better idea, one that doesn’t require modifications to the lower at all. I got out my tube of Plastic Steel Epoxy. If you’ve never worked with this stuff, it is basically powdered metal mixed with epoxy resin. Like all such products, you mix it with a hardener and will stick to just about anything (including cleaned and degreased steel or aluminum). When fully cured, it can be machined like metal and even drilled and tapped – great stuff for fixing stripped-out screw holes in a gun frame.

In this case, I just ran a little bead of it along the bottom of the magazine catch – just the pin end, not the catch end. The catch that engages the magazine slot itself was the correct size, so I didn’t want to change it. I just needed it to be supported enough to maintain the correct position. These pictures show what it looked like after curing and then filing and fitting to match the slot.


Filing and fitting took the most time, but I was pleased to note that the cured product matched the color of the part almost perfectly. Once installed (see picture below), the fix was almost invisible.


It looked OK, but did it work? On the bench, it seemed to be good with the magazine latching properly when pushed all the way in, and no movement of the mag once the latch was engaged. But I wasn’t going to be satisfied until I actually tested it, so back to the range again (and again with the good ammo).

Perfect! Feed, shoot, cycle – no problems. Ran several magazines through it without a single feed issue or misfire. Took it back to the shop and cleaned it up, and also removed and checked the magazine latch to make sure it wasn’t showing any problems. Called the customer and gave him the good news (and my bill).

Yes, I have to love those ARs. I never know what I’m going to see tomorrow but I’ve yet to find a problem with one that couldn’t be fixed. Some fixes just require a little more creativity than others.

13 Responses to AR-15 Issues… You Never Know What’s Going to Walk Through the Door

  1. Good “catch” John. Excellent article. I never had or used an AR 15 but I think the two narrow photos are not showing enough for what you are explaining? Pardon me if I’m wrong.

    The plastic steel epoxy sounds just like the JB steel weld epoxy I bought to use for same reasons as you mention (have no TIG). The JB steel weld epoxy mixes and cures greyish. I have some brown and black dye that came with a bedding epoxy I used once mixed into the JB steel weld since it was used to apply to a black polymer trigger plate. A drop or two of dye goes a long ways and the weld worked great for gluing metal into plastic.

    Anyhow, I have a question for you about this steel weld you use: The hardener and resin need to be mixed in equal parts (in which you know). It seems when I mix it and when it is cured and then filed or drilled it is flaky/dusty like wood would behave. The stuff dries hard though. You said your steel weld files like metal. I eyeball my mixing ratios since I usually only need a small amount, so I am wondering if I am mixing unequally? Was curious your thoughts about this. I will try using a measure next time I mix some.

    I originally bought this steel weld in hopes to use it to fix sloppy op/charging handles on .22 rimfire semi-auto rifles but the stuff just hasn’t cured like metal and I do not want it to flake off and get into the action.

    Thanks John, well written article. Cheers!

    • The stuff I use is a Devcon product, but I believe it is very similar to the JB Weld product you are talking about. It actually comes in several different colors including silver and the dark grey I am using here. As for “machining” it, I used both needle files and sandpaper to get it down to where I wanted it, and no… it doesn’t behave quite like metal — not nearly as hard. It actually feels more like wood in terms of sanding and filing, though it will retain a pretty sharp corner or edge. They say it can even be drilled and tapped, but I haven’t had a need to try that yet.

  2. The -out of spec- lower receiver needs to be brought to the attention of the manufacturer for replacement -on their(manufacturer’s)dime-,mind you.
    Selling the customer a suitable replacement was an acceptable “fix” to get the customer satisfied and on their way, but the customer also should be counseled on the need to bring “junk production” to the attention of the manufacturer’s customer service department.

    • The primary issue there was that the customer didn’t buy it new (in fact, he didn’t buy it at all — he swapped it for an old trailer) and the gun had been mix-and-match put together in the first place. Manufacturer had a perfect excuse to say it had been modified by someone and all bets were off. The lower was actually a well-known brand, and I haven’t seen others with the problem. In fact, this was the first time I’ve seen a problem like that on anyone’s lower. In any case, the customer was happy with the fix.

  3. Great article, thanks.

    I had a customer bring in an AR a couple months ago. He had attempted to replace the stock pistol grip with one that fit him better. Simple enough, but he somehow managed to ruin the threads in the lower receiver. I bought a thread repair kit (1/4-28) at my local industrial supply. It came with the proper drill size, tap, a bunch of thread repair coils, and installation tool to install a coil insert. The receiver now has nice new 1/4-28 steel threads that should be harder to cross thread.

    • Yeah, the AR does offer the amateur gun-builder lots of opportunities to screw up the one part you can’t just replace. Haven’t had anyone mess up a pistol grip installation yet, but I’ll sure keep your solution in mind if I do get one.

      I’ve actually built an AR (for myself) using a polymer lower, and so far it has performed well and is holding up to lots of use. As I was building it, though, I remember thinking how easy it would be to damage that silly piece of high-tech plastic.

  4. I have assembled many ARs and have only had two that had issues after assembly. The first one with a problem was a mil spec barrel I had bought. After disassembling and reassembling several times because it would short cycle, I found the gas port in the barrel had been drilled too small. I opened it up and the AR was cured. The second one I had a problem with would fire fine for about 5 rounds then the bolt would not close and lock on a round. Turns out the chrome trigger assembly from Anderson was a reject. I replaced the trigger assembly and was good to go.

  5. I found a brand new Ruger AR that would not cycle the bolt completely. First thought was that the actiob needed some lubrication. Then the owner said that a pin had fallen out of “somewhere”. Looked around the shooting bench and found a pin.
    That pin had held the front sight base loosely in place. The sight base moved with each shot and covered the gas port.
    Had to reset the one pin so the fellow could finish his magazine.

  6. Love the article and remedies. I will tell you that a hands down better fix for the stripped out screw hole is a product called Time-Cert! It is used mostly in automotive use but is better than any piece of wire coil. It is solid black oxide steel and it more expensive than “helicoils” by far but will not pull out and is set with RED Loctite. These things are incredibly tough and I have used them on many occasions. It can be machined when set and has a shoulder built in so it fits flush. The kit comes with inserts, drill bit, chamfer bit, and install tool. About $134.00 for any specific kit, so yes it’s expensive but you also don’t have to buy the bit separately like you would with the helicoil kit, and no little wire to have to try to snap off when installed. BIG plus there! Also much easier to use and 100% more reliable.