This is an AR pistol that a customer picked up at a gun show. He brought it to me to look over and address any issues that it may have. While it may look fine at first glance, I would not be doing this article if it was.
The first thing that I noticed was that the castle nut was not staked. While it is not absolutely necessary to stake the castle nut, it costs nothing and doesn’t take long to do. If the person doing the assembly doesn’t care to take the time to do this simple step what else did they skip?
Well apparently using a proper 3/4″ inch wrench to attach the flash hider was just too much. Not exactly sure what they used. Pliers of some sort is my guess. Channel locks or locking pliers most likely.
For those of you not familiar with this platform, the gas tube should NOT go down towards the barrel.
No clearance for the gas tube. Not a problem for the person doing the initial assembly, just use a rabid beaver to chew a hole in the handguard.
What goes down must go up……………….eventually. There are supposed to some bends in a gas tube. This is NOT one of them.
These are what I was able to find by just doing a quick inspection on the outside. It didn’t get any better once I opened it up.
By the looks of the buffer, that beaver was not full after chewing on the handguard. These marks are the result of the buffer hitting the retainer during firing. The buffer should only touch the retainer when the upper and bolt carrier are not in place. The bolt carrier should push the buffer off of the retainer when closed. There are a couple of ways to check for that this. With both the takedown and pivot pin pulled out the upper should be pushed away from the lower by the buffer. Another way is to remove the charging handle, replace the bolt carrier, close the upper and you should be able to see the buffer move. I tried both of these tests and it passed. So here is another short cut taken by the builder. They took a chewed up buffer that they didn’t want and put it in a gun that they were getting rid of. Are you starting to notice a trend that started with the lack of staking on the castle nut.
This is the back of the bolt carrier. There doesn’t appear to be any obvious burrs or deformations that would cause the marks seen on the buffer.
Staying with the bolt carrier, I checked the screws holding the gas key on using the reverse torque test. Proper forward torque should be approximately 55 in-lbs. The reverse test starts at 25 in-lbs. One of the screws came loose at that range. The next step is 35 in-lbs. The other one failed here. The staking here was also almost nonexistent. If your gun shows signs of being undergassed, and you see carbon built up at the front edge of the gas key then have it checked out.
You can see by the shiny spots that this gas key was starting to move on the carrier. There’s a little carbon built up around the gas port but it has not made it to the sides of the key, so there were no outward signs that this was coming lose. This issue was caught before it became a real problem. Lose screws have a way of becoming broken screws.
Results of the first few passes on a diamond plate to “deck” the gas key. If I had just simply tightened the screws back down it may have still leaked in the future.
Finished “decking” the gas key. We are limited to fixing only this piece because of the way the carrier is machined. I use a bearing retaining compound to fill in any remaining imperfections in the mating surfaces.
These pictures show the retaining compound squishing out, and the new “OCKS” used to secure the gas key. (Optimized Carrier Key Screw from Michiguns Ltd. http://www.m-guns.com)
Using a MOACKS Plain also from Michiguns Ltd. to properly stake the gas key screws.
(Mother Of All Carrier Key Stakers)
The OCKS give a place for the metal that is displaced by the staking a place to go and keep the screws secure. The burrs that caught the fibers from the rag were eventually removed.
Original extractor spring and insert. Since there were other suspect parts in this gun it just made sense from a reliability standpoint to replace it.
In the image to the right the original extractor spring and insert is on the right, the Sprinco 4-Coil spring and insert are on the left. https://www.sprinco.com/
Next I checked the gas rings, they seemed fine and were reinstalled
This is the ejector after polishing. Didn’t take a before picture, but it had a pronounced projection from the machining. It would have eventually scraped brass from the bottom of the case. That could have ended up down the bore that the ejector is in causing poor performance or even a malfunction if the case is not pushed clear of port fast enough.
Original ejector spring on the right, new on the left. The original may have been fine, but for few dollars a new one cost, it was better to replace it. With the ejector and spring out I checked the headspace and it passed.
The next check I performed was to see if it actually has a 5.56 NATO chamber and throat. This gauge from Michiguns Ltd.checks for that.
To start I “Sharpied” the end, to show if there was any interference.
The gauge is then pushed lightly into the chamber. It should fall out if the throat is the proper size. Go figure it got stuck in this one.
The white line in the ink is where the gauge made contact with the throat. This barrel did pass the “plunk” test with some factory ammunition so I didn’t try to fix this.
If you look at the feed ramps in these photos you will see that the center locking lug protrudes into the feed ramps cut into the upper receiver. This can cause malfunctions by catching either the bullet tip or the edge of the case as it’s trying to feed into the chamber. There are also some machining marks still visible.
The major work on the right side is done, and the left is almost done.
Here the ramps are all finished. Nothing to snag on.
Judging by the carbon ring it appears that the gas block was slightly misaligned.
The barrel is not dimpled so there was no place for the set screws to index in.
Using a jig I added a dimple. The picture is before I reblued the surface.
New gas block and tube installed.
New gas tube on top. Original on the bottom. Muzzle end would be on the left.
Closer look at the chewed up flash suppressor. In this image you can see that the crush washer has been installed backwards. The muzzle device was not tightened to specs either.
This is why I couldn’t see the crush washer with the handguard installed. Speaking of the handguard. The following images may be disturbing, if you care about how your firearm is assembled.
This is the bottom of the handguard. Not really sure why they went after this area. Probably the mildest definition of a mistake. It gets worse from here.
You were warned.
After looking at this closer. It appears that this handguard is for a blowback operated platform since it doesn’t have channel for a gas tube. That didn’t deter someone from making one. Not sure how long it took to make this disaster, but it had to go. Now that the upper and barrel are fully disassembled it is time to start bring this thing back to life.
The gas block was previously installed. Here is the new Midwest Industries Pistol Blast Diverter.
Installing the new handguard. A Midwest Industries 10.5″ Slim Line Handguard.
Back up Iron sights reinstalled.
Completed upper with Holosun Red Dot installed. This is much better.
Next was to address the lower receiver. For the most part there were no major issues found. Just the buffer and the non-staked castle nut.
The roll pin for the trigger guard was a little above the surface of the ears. That was a quick fix.
The hammer and trigger springs were okay, so they were reinstalled.
Added a set screw for the take down pin retaining spring and detent. This will keep the spring from coming out unexpectedly, should the endplate be removed.
Torqueing the castle nut to 40 ft=lbs.
Castle nut staked in 2 places, as per the manual.
Here’s the completed rifle getting a final cleaning before being returned.
Added a Blue Force Gear Sling and Midwest Industries Swivels.
Business end of the Blast Diverter.
Streamlight Pro-Tac Rail Mount HL-X with Laser. 1000 Lumen light with built in laser.
The finished product. Short, light, reliable, what else could you ask for.