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The “Frankengun.”

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.

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.

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.

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First Customer Build: The Upper

Back for the second half of the build.

The stripped upper on a bench block preparing to install the forward assist.

Completed upper with the tags for the parts used. The customer is left handed and may run the charging handle from the right side. In that case the use of the FCD Low Drag Forward Assist means less chance of scraped knuckles during a malfunction clearance drill.

A view showing how minimalist this forward assist is.

Before and after of the feed ramps on the Criterion Barrel.

Initial dry fit of the barrel to the receiver. Went back and opened up the right edge of the right ramp. The left ramp was okay. Don’t really want to take the anodizing off the ramps in the receiver as that makes them prone to being damaged.

Prepping the bolt to check headspace. This fixture makes it easy to remove the pin holding in the ejector. The ejector can give a false feel during the headspace check.

Stipped bolt ready to check headspace.

My headspace gauges are on the bottom of the picture. Since this picture I have added a proper 5.56mm headspace gauge. The barrel did pass the .223 Remington GO gauge. It also passed by not closing on the 5.56mm max gauge.

Nicely dimpled by Criterion

SLR Jig to add a second dimple. Why? Because your gas block can’t be too secure.

After the jig.

Cold blued he spot for appearance and corrosion protection.

Used Loctite 620 Bearing Retainer to bed the barrel to the receiver. The bearing retainer will swell slightly, filling any excess space, and lock the the two together improving the rifles consistancy.

Barrel and receiver hand tight. Waiting for the bearing retainer to set up.

Gas Block

Installing the Sionics Mid-Length gas tube.

Just enough of a second dimple for the set screw to dig into.

Original set screw.

The knurled set screw I actually used. In addition to the knurling I also used VC-3 to insure the screws don’t loosen.

Torquing the barrel nut on the Midwest Industries Slim Line Combat Rail to 40 foot-pounds. This is the 15 inch version. I really like that the barrel nut for this line of handguards doesn’t need to be timed to the gas tube.

Torquing gas block set screws to 30 inch-pounds.

Fully assembled gas system.

Testing that the BCG not impeded by the gas tube. It passed with no interference from the gas tube. This will maximize gas tube and gas key life.

Customers choice for a muzzle device.

Hand tight to the crush washer.

Tightened till the marks aligned.

Almost finished. Most of the hard stuff is on.

Even though its probably not needed. I still used the rail alignment fixture to make sure the rails are straight.

Torque tab installed. Keeps the handguard from coming off and prevents over-tightening of the screws.

Setting the torque.

Following instructions.

Assembly complete. only a few more parts to add.

Starting top see what the final product will look like.

This is one of the last parts.

First assembly. Hope the customer likes it. Just have to add a few accessories.

Its not loaded. Just waiting on BUIS from Midwest Industries.

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First Customer Build: The Lower.

This is how a build starts, with just a stripped receiver. For this build I will be using a receiver with my company engraved on it.

Started with the Low profile Magazine Catch from Forward Controls Design (FCD).

Paired it with a Enhanced Magazine Release also from FCD.

More FCD parts. This time their Augmented Bolt Catch/Release. The pads are a little bit bigger and slightly angled to manipulation more positive.

Next up were the take down and pivot pins. These pins from FCD are .040 longer than normal and made of better steel. It may not seem like much, but that extra length is appreciated when all you have are your knuckles to knock those pins through.

Here you can see the set screw used to capture the spring for the take down pin and the VC-3 from Vibratite. The screw keeps the spring from getting launched into the great beyond, should the customer chose to change the end plate and not realize there is a spring there. The VC-3 is used to keep the receiver extension from possibly rotating during castle nut torquing, or during hard use. It’s not as “rigid” a connection as Locktite type products would be, in that you can still adjust the parts after it has set up.

The receiver extension ready to be installed. I used a castle nut from FCD, which has more and deeper notches allowing for more secure staking. Grease is used in order to get the proper torque value and to prevent galling between the dissimilar metals. The end plate is from Midwest Industries and has a QD socket in it. I like to include this version in my builds so that the option to attach a sling at the rear of the receiver is already there.

Just waiting for the VC-3 to set up overnight, and the packaging for the parts.

Receiver Extension fixture used to torque the castle nut.

Mark from spring loaded center punch.

First stake finished.

Start of the second stake.

Second stake finished, as per the manual. Don’t have to worry if this will come apart under hard use.

Bravo Company Manufacturing (BCM) Trigger Guard. The button head screw for the front is an idea I got from a builder page on Facebook. I think it looks good enough to make it a standard for polymer trigger guards.

Checking the springs on the ALG Defense QMS Trigger.

Trigger and disconnector installed. The grease is on the sear surface. You may also notice how the bolt catch tilts away from the receiver a bit more than normal.

A lot of work since the last picture. Forgot to take pictures a long the way. The hammer has been installed and being tested against the block. For parts longevity avoid dropping the hammer without some sort of cushion. If you let the hammer fall full force against the receiver wall or the bolt catch it can damage them over time. You can use your thumb, foam ear plug, or a purpose built block like I have here, just slow the hammer down some how. This only applies when bolt carrier group is not there to take the blow. Such as this picture when both halves are not attached or when the receivers are “shotguned”. Most AR rifles should not be damaged by dry firing in an assembled condition, like used for reinforcing marksmanship fundamentals.

The pistol grip is also from BCM it is the MOD 0 version since the end user has small hands. This will manipulating the controls a little easier.

The safety you see here is not the permanent one its just a place holder until the ambidextrous one comes in.

After the addition of the Magpul CTR stock the lower is finished. I will cover the build up of the upper receiver in another post.