SHTF Armorer: The AR-15 BCG

Whether you like it or not, you have to admit that the AR-15 is the rifle of choice for the majority of preppers nationwide. It’s adaptable, it’s easy to handle, easy to shoot well, and the sheer numbers of them out there mean that any prepper undermost circumstances should probably have one in his arsenal.

If you DO have one, you should know how to work on it.  You may love yours to bits; you lovingly selected every part, widget, accessory, and optic on your AR. But if the balloon goes up and yours breaks, you can’t exactly roll down to the local gun shop and expect the gunsmith to fix your problem while you wait. You may find a parts gun in an abandoned police cruiser or National Guard armory that will work on your gun (most are Mil-Spec and therefore mostly interchangeable)…but who’s going to work on it? Guess what, buddy: you are. Luckily, the AR platform is pretty easy to work on.

I keep a smattering of easily-replaced (read: field-replaceable with little or no tools) parts in the Magpul ACS stock compartments of my go-to rifle, along with a cut-down 1/16″ punch, which lets me work on most of my AR with maybe a convenient rock utilized as a hammer. But those parts and punch are useless without knowledge.

What’s that? You have an AR as your go-to SHTF rifle and you can field strip it, but really not much else? Well, let’s start fixing that problem. And we’re going to start the process with learning about the most crucial element of the AR-15/M4 system: The Bolt Carrier Group, or BCG.

First, we’re going to assume that you can remove your bolt and charging handle from the gun in the normal field-stripping procedure.  Do so. You’re going to need a couple specific things, one of them being a 1/16″ or 3/32″ drift punch…this should be relatively easy to come by at your local hardware store. Make sure you get a good hardened one; cheap ones bend and snap very easily. A small hammer will probably be needed, as well as a few cleaning patches, a bunch of Q-tips, some gun cleaning solvent, a light, high-quality gun oil, and a small scraping tool (I use a jeweler’s screwdriver.) A dedicated AR-15 multi-tool is a godsend; I heartily recommend one! Let’s get started.

Disassembly

First, we’re going to pull out the Firing Pin Retaining Pin. This is a small, cotter pin-like affair that is recessed into the side of the bolt. Using a punch, pry it out.

A word about this pin: it is a hardened pin; if it breaks somehow, you’ll need to get another AR-15 specific pin. Just going to NAPA and getting a cotter pin won’t work. Those are soft, malleable metal and will break very quickly. Firing Pin Retaining Pins are cheap, so there’s no reason not to buy a few of these expendable parts and have extras.

This pin, as the name suggests, retains the firing pin in the bolt housing. Removing it allows us to pop out the firing pin, which, depending on your level of gunkiness, may drop right out, or need to be pried out.

Next, we’ll get the bolt proper out of the carrier. To do so, we need to pull out the Bolt Cam Pin. Push the bolt head backwards into the body of the carrier (you’ll see it moves back and forth), and once it’s fully in, the cam pin can be turned 90 degrees in either direction.

Once the cam pin is rotated 90 degrees, pull it straight out of the bolt carrier body. It should come out easily.

Once the Cam Pin is out, the bolt can be pulled from the carrier body. If your gas rings are fresh, the bolt may come out a little tightly, but it should pop out with no real problems.

To disassemble the bolt, there are two pins we need to remove. Grab your trusty pin punch, and drive out this pin to remove the extractor. Be careful: the extractor does have some spring tension behind it, so keep your thumb on it to keep from launching things.

Remove the extractor slowly, watching the spring tension, and set aside. We’ll get back to that in a second.

Next is the ejector. I usually don’t pull out the ejector on routine tear-downs, but it’s easy to do. Drift out the tiny roll pin indicated below (keeping your thumb over the ejector! Serious spring tension here!) and pull the ejector and its spring out of the front of the bolt. Take note of the orientation: There is a notch in the ejector for the pin, and it needs to go back in the same direction it came out so things will work properly.

I also don’t pull the gas rings off – there are three of them; you can see them as a slim silver band towards the rear of the bolt body in the picture below. If you need to remove them, use a dental pick or something similar to pry them out of the groove, then peel them out one by one. These rarely need to be replaced unless the rifle is seriously malfunctioning, so I leave them alone generally.

The extractor houses a couple extra parts: the extractor spring, the extractor spring buffer that resides inside the extractor spring, and usually a rubber O- or D-shaped ring that sits around the extractor spring. This O-ring really helps the extractor spring out in the power department, and it’s easily retrofitted if yours doesn’t have one. The Extra Power upgrade kit is, once again, very inexpensive, and cheap insurance against failures to extract. Grab a couple and keep a spare.

Another item, the last part of the bolt, is on the carrier body, and it’s called the Bolt Carrier Key. It’s held in by two cap screws that are heavily staked in. You can see it in the first photo of this article, where the Firing Pin Retaining Pin is partially pulled out. This key allows gas into the bolt, and it must be sealed strongly on the bolt. Make sure it is secure on the bolt carrier and that you can’t see daylight between the bolt carrier body and the key. If you can, it’s letting action gas be wasted, and needs to be replaced. But if it’s not wiggling and if you can’t see daylight under it, leave it alone.

Cleaning

There are a few words to be said about properly cleaning an AR bolt. As a direct gas impingement system, hot gases and carbon from the cartridge firing are directed right into the body of the bolt, and as such, it gets very dirty very quickly. With all the crud being subjected to lots of cycles and lots of heat, it quickly builds up and hardens inside the bolt. If not properly cleaned, it builds up to the point where the firing pin won’t work properly, or the bolt won’t go fully into battery, amongst other things. So therefore, it is imperative we do a little bit of extra maintenance inside the bolt while it’s apart. Gas piston AR guys don’t have to worry as much about carbon buildup, but it’s still important to keep the innards of your AR bolt carrier group properly clean.

Let’s start with that extractor. The groove in the underside of it catches the rim of your case and pulls it out of the chamber. If that groove has crud built up in it, the extractor cannot properly grasp the rim of your expended cartridge, and you will have a failure to extract, probably followed by the next round from the magazine being fed into the back of the case that didn’t extract. And that, my friends, is a whole lot of suck.

We can prevent that from happening by simply cleaning the extractor groove. Take a small screwdriver, a toothpick, dental pick, whatever – and scrape the gunk out. Use a Q-tip with powder solvent (such as my old friend, Hoppes #9) to break things loose if it’s really built up.

Use a Q-tip or two and clean out the extractor cutout in the bolt body for good measure. I will put a very, VERY light coat of oil or none at all in the extractor cutout. Oil attracts dirt and grime, and dirt and grime will impede the extractor from properly actuating in its cutout. I do, however, put a drop of oil in the hole the retaining pin goes through, so it will pivot freely when assembled.

When cleaning the bolt, you need to get all the built-up hardened carbon off the “tail” of the bolt, as shown above. I soak it down with Hoppes # 9 or a cleaning patch, then scrape it away with a small screwdriver. This is one of the important areas on an AR bolt: if this is allowed to build up with carbon, it will eventually impede backwards progress of the bolt in the carrier body, and the gun will not function. Use a Q-tip and clean out the hole for the Bolt Cam Pin, and all the locking lugs on the head of the bolt. Clean the bolt face as well.

Make sure this end of the bolt head is nice and clean as well.  (Yes, I know the BCG is assembled.)

When cleaning the firing pin, make sure all the carbon is cleaned off of it. Again, if it’s loaded up with grime, it doesn’t free-travel inside the bolt and the gun will not function.

When cleaning the Carrier, pay special attention to the areas inside. Carbon builds up like crazy inside of the carrier, and it all needs to get out. I soak this puppy with Hoppes for a few minutes, scrape it with a screwdriver, and usually blast it right out with Gun Scrubber or non-VOC brake cleaner.

I make sure the bolt is nice and dry, with no cleaning solvent residue anywhere, inside or out. I will usually heat the big parts (bolt and carrier) up inside my oven (don’t tell my wife) at about 170 degrees to open the metal’s pores up, then I’ll use Militec-1 or FrogLube or a similar metal-penetrating lube oil lightly on these parts, inside and out. I let them cool completely to close the pores, then thoroughly dry off the excess, with just a light coating of lube on the outsides of the parts. The main thing is not to leave enough lube on the parts to attract dirt, sand, etc., but to have enough for the parts to not wear as they actuate, nor corrode if they sit for a while. I put a drop of high-quality gun lube (like the aforementioned Militec-1) on the Bolt Cam Pin as well. I like to leave the firing pin clean and dry, with no lube on it to attract anything that will impede its moving freely.

Reassembly

The bolt is kind of a reassemble-in-reverse-order setup. Install the ejector (if you pulled it), then the extractor and its spring, buffer and O-ring. Put the bolt back into the bolt carrier, making sure the extractor will be facing the ejection port of the rifle once it is installed. This is important for the function of the rifle. If the bolt head is in 180 degrees off, the ejector will punch the fired cases back INTO the rifle instead of out of the ejection port. We don’t want this, for obvious reasons.

Insert the Bolt Cam Pin as you took it out, rotate it 90 degrees so it will clear under the gas key, and then install the firing pin into the back of the bolt. Make sure it slides back and forth freely, then install the Firing Pin Retaining Pin in the side of the bolt.

The bolt should slide back and forth, and rotate freely in the carrier, with some resistance. To test if the gas rings are good, extend the bolt fully out of the carrier, then set the bolt down on a table or flat surface. Gravity should not let the bolt carrier slide down on the bolt; it should stay fully extended. If it does slide down, it’s time to replace the gas rings on the bolt body.

That’s about it! Re-install the bolt and charging handle in your rifle, and make sure everything functions as it should. Then go shoot the hell out of it and get some training!

Questions? Comments?  Anything else you’d like to know about the AR platform in an article? Let’s hear it in the comments below!

Stay safe!

-TRW

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