Building a 12.7×42 (.50 Beowulf) 7.5″ Pistol – The Wulferine: Post 3 – Handguard, Gas Tube & Brake

In the last post, I covered installing the forward assist button and the ejection port cover. In this post, we’ll proceed with installing the Midwest Industries 7″ Combat Rail, gas tube and the Satern helical muzzle brake.

Special Assembly Note

Here’s some hard won advice I want to share with you. When you install the barrel nut and the muzzle brake, there is significant torque involved. You absolutely do not install a magazine well block in a vise or clamp the upper directly — You will bend or break stuff. For example, the alignment pin on the barrel will let go – and has done so to tons of people who didn’t secure their upper properly … Spend the money to get the right tool.

Here’s my personal experience: Years ago before I knew much about ARs, I had one of those little jigs that puts pins through the takedown and pivot pin lugs – I think I got it cheap off Amazon. At any rate, I was trying to remove a bird cage muzzle brake that was on real tight and managed to bend the takedown lug of the upper and that was the end of me using those. Yeah, I was ticked and then I started asking around what tools/jigs folks were using.

There are two options for you that I can recommend. Personally, I use a Magpul Barrrel Extension Vise (“BEV”) Block with a bolt carrier to secure it. It has steel lugs that engage the barrel extension and a full-length steel shank for strength. I’ve used many times over the years and it hasn’t let me down.

This photo is from my last Beowulf rifle build. The BEV block is to the left of the bolt carrier. You slide the BEV block up through the mag well and forward to engage the barrel extension. The bolt body comes from the rear and a pin goes through the hole you see to secure the block via the pivot pin hole on the upper. It’s nice and solid. Magpul sells you the block but you need to supply the carrier. You could either have a spare sitting around just for this, which is what I do, or remove the bolt from your carrier and use it. The carrier is not harmed in the process.

Your other option is a Geissele Reaction Rod. I’ve heard good things about the Geissele rod but have never used it. Guys who have it gush about it and you know how fast guys are to complain when a tool sucks.

You can usually find either at Brownells, Midway, Primary Arms, PSA, etc. There’s a lot of back ordering going on these days so you might need to hunt some.

Midwest Industries 7″ Combat Rail

Let’s roll right into the handguard discussion because we will need the barrel nut to install the barrel first. With the advent of the free floating handguards, meaning the handguard does not touch or push on the barrel affecting accuracy, makers started creating their own barrel nuts that their handguard would attach to and the nuts vary dramatically in terms of design.

My favorite AR free floating handguards are the Midwest Industries (MI) Combat rails. They are very well made, rugged, easy to install and all the surfaces that can poke or nick you have been rounded over. I’ve installed four of them now and really do like them.

For the 7.5″ barrel, I opted for a 7″ rail to allow for the muzzle brake to poke out the end and vent properly. I also only use M-LOK attachments now and the Combat rail has those.

The MI Combat rails come with installation instructions that are quite detailed. Take the time to read them before starting. If you have questions you can either contact them or do some quick searching. In general, a little bit of time spent preparing can make things go far more smoothly.

To install the rail, the first thing to do is to disassemble the rail – Midwest Industries ships the unit with the barrel nut, torque plate and two screws installed so you can see how it goes together plus it keeps everything tidy.

After you remove the rail from the box, you will need to disassemble it. I put all my small parts in a magnetic try to avoid losing them. Top left of the rail is the barrel nut, below that are the two 10-32×1/2″ allen head handguard screws and below them is the torque plate that limits the handguard’s forward travel. It’s really an elegant design. The biggest benefit is that you can torque the handguard down to MI’s 40 ft/lbs and there is nothing that will get in the way of the gas tube being installed.
Slide the barrel into the upper making sure the index pin on the barrel goes into the corresponding groove on the top of the upper. Coat the threads with Aeroshell 33MS/64, or equivalent grease, and hand thread the barrel nut into place. The slots on the barrel nut must be facing the end of the barrel as pictured. Note, different builders use different greases and some use one of the various non-seize compounds. I have a small container of the Aeroshell 33MS/64 grease just for this purpose and lightly apply it using an acid brush (these are small still brushes used to apply acid flux (hence the name) and are handy for many tasks such as this). The checkering on the but will allow the relatively soft aluminum rail to get a very secure grip when the two clamping screws on the rail are torqued down later.
Follow the directions for installing the BEV Block. You can see the bolt carrier sticking out the rear and a 1/4″ clevis pin going through the pivot pin hole to secure the assembly. The reason for the universal clevis pin is that I lost, or maybe I should say “temporarily misplaced” some time last year, the original pin that came with the block. The 1/4″ clevis pin works just fine.
You will need to secure the upper in a good bench vise to torque down the barrel nut. This is why the BEV Block rocks. As long as your vise is secure, so is the upper. The torquing stresses are handled by the engagement of the BEV Block into the barrel extension – not the aluminum upper. This is a Samson vise that belonged to my dad – it’s heavily ,made and bolted to the 1-1/2″ thick work bench.
To properly install the barrel nut, you need a torque wrench. “Farmer tight” is not recommended. Per Army manual TM 9-1005-319-23&P, proper assembly is to torque the barrel to 30 ft-lbs, loosen and repeat three times. This stretches the threads and reduces the risk of the barrel nut loosening up. The Midwest Industries installation instructions specified 40 ft-lbs so I torqued to that spec and loosened it three times. Note, they supply the special barrel nut wrench that then engages with your 1/2″ torque wrench. I use a Tekton 24335 torque wrench for this and am always sure to rest it to zero before putting it away.

Pistol Length Gas Tube

Once the barrel nut has been installed, the gas tube is easy. I bought a 0.875″ diameter gas block and pistol length gas tube from Satern. They make a single divot on the bottom of the barrel so when you slide the tube into place and tighten the set screws, the gas block is properly located. The installation is easy – slide the block on with the tube going into the hole made for it at the top of the receiver.

In this photo, the upper is upside down clamped by its Picatinny rail in my wood working vise. A wood vise is darned handy when you want to work on things and not tear them up. This is a big 10.5″ Yost with maple jaws. At any rate, you can see the bottom of the gas block and the two set screws. Coat them with a medium-strength thread locker to reduce the odds of vibration shaking them loose. The set screws should be torqued to 20 inch-pounds per Satern – that is inch-pounds and not foot-pounds!! Note the slight gap between the right edge of the gas block and the shoulder of the barrel. That should be there and it should measure 0.025″ with a feeler gauge.
You can get feeler gauges many places – notably auto parts stores. Here, I have the 0.025″ leaf, or blade depending on who you talk to, extended. It should slide into the space with just a bit of resistance as it touches the sides but the next larger size should not if you are aiming to be on spec. I was told to hit 0.025 so that’s what I confirmed. Sometimes people will give you a range and in those cases, you just want the gauge that fits to fall in that range.

Satern “Heliport” Muzzle Brake

Because this is a low profile brake, you can install it before or after the handguard. If you are installing a tanker brake, you’d do it after the handguard. In my case, I opted for before.

Remember what I said earlier. You need a jig to properly hold the barrel or something will brake. In this case, you run the risk of the index/alignment pin on the barrel shearing off or bending the receiver. Don’t do it.

Installing the Handguard Itself

At this point you should have the barrel installed, the barrel nut installed and torque down as well as the gas tube. Installing the handguard is actually quite simple. You slide it back onto the nut with the “ears” aligning it to the upper’s rail. You then flip the receiver upside down, install the torque plate, apply thread locker to the screws, install and torque them down to 55 in-lbs.

Here, I’ve pushed the rail back against the upper. You can see the alignment “ear” on the rail stabilizing the rail against the upper. I’ve not needed to adjust these. The bottom two holes just forward of the protruding clevis pin are where the two 10-32×1/2″ socket cap screws will be inserted after the torque plate is installed.
This photo turned out better than I hoped for. Through the slot in the rail you can see the barrel not. Note how the groove in the nut is towards the front. The torque plate that ls laying on the rail is asymmetrical for that reason – it will go down with the protrusion entering the slot. Note the raised dots that will lock the plate into position when the two clamping screws are installed. Seriously, these details play a big part in why this is my favorite AR handguard.
WIth the torque plate installed, put medium thread locker on the screws and install them. I like to bring them down equally snug and then torque to the specified 55 in-lbs using a 1/4″ torque wrench. Once installed, the rail is good to go.

Install The Bolt Head

I bought the bolt head from Satern and it needed to be installed in a carrier. Luckily I had some spares from cases where I swapped out bolts for WMD NiB bolts. I opted for a carrier with a nice smooth nitride finish and installed the head. Note, during assembly I apply a thin coat of Super Lube grease to all sliding parts. I’ve found it’s a great break in lube.

The Satern 12.7×42 bolt head (bottom) installs in a 5.56 carrier with no fitting needed. Assembly and disassembly are the same as any other AR bolt carrier group (BCG).

Install The Charging Handle, Bolt Carrier Group & Done

I installed the BCG and BCM Mod 3 charging handle into the upper and with that, the upper was fully assembled not including any sights or optics.

In Conclusion

That concludes building the 12.7×42 (.50 Beowulf) upper. In this case it would attach to any AR-15 sized pistol lower that you have. Click here for our past posts on building AR lowers.

I hope this series has helped you out!


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Sources For AR Parts

The following are all vendors of AR parts including barrels, handguards, triggers, magaziness and what have you that I use and recommend:

Beware no-name knock off websites selling generic import stuff. Some of the parts are counterfeit and not rated for firearms use.