Category Archives: .50 Beowulf – 12.7x42mm

Changing Springs and Buffers in My Beowulfs To Improve Reliability

Okay, so the last range trip went a lot better. The new Lancer L5AWM mags with Tromix followers worked great. The reliability on the pistol was coming along but not where I wanted it and the rifle was disappointing still but I knew what was going on.

7.5″ Beowulf Buffer Spring

My 7.5″ Beowulf pistol is running pretty well but I wanted to increase the forward force of the bolt carrier to strip the next round and chamber it. I was already running an H2 buffer but an other wise normal carbine spring. I upped my game to a Sprinco Red Extra Power Carbine buffer spring that they say is made with the “thumper” cartridges such as the .458 SOCOM, .450 Bushmaster, .50 Beowulf. I bought mine from Primary Arms.

The Mil-Spec Carbine Buffer Spring is on top. The Extra Power spring is on the bottom with one end painted red. That’s handy for knowing what spring is in the weapon at a glance.

I cleaned the pistol, lubed everything and installed the extra power spring and the H2 buffer that was in there. It definitely slammed home harder when I released the bolt.

When we go to the range next, I’ll be taking a standard carbine spring, an enhanced Sprinco spring and the carbine already has the extra power spring already installed. I’m also taking standard, H2 and H3 buffers with me.

Changed the Spring and the Buffer on my Full Size Beowulf Rifle

This rifle was built using an Alexander Arms DIY upper.

When we were shooting this, it had a hard time stripping the next round and chambering it. It dawned on me that they hydraulic buffer that I originally used wasn’t driving the bolt carrier forward hard enough. You see, a Hydraulic buffer has a piston inside that has a controlled leak down rate and, for whatever reason, it was dampening the stripping of the next round properly.

With carbine tubes, you have tons of sling and buffer options. Not so much on rifle length tubes. I did opt for a Geiselle Super 42 rifle-length buffer spring and a slightly heavier Expo Arms 5.4 oz rifle buffer –I bought both from Primary Arms.

Top: KynSHOT hydraulic buffer and Mil-Spec rifle-length buffer spring.
Bottom: Expo Arms 5.4oz buffer and Geiselle Super 42 Rifle-length buffer spring
The Kynshot buffer is very nicely made but I don’t think it’s the best choice for this application. I will save it for future projects.

When I cleaned the rifle prior to installing the new spring and buffer, the one surprising thing I found was that it was fairly dry. Why? I have no idea and this would have impacted functionality at the range also as I assumed I’d lubed it already before putting it away. Yet another example of my memory not being what it used to be.

Given that surprise, I went through and applied Super Lube oil and grease before installing the new Geiselle spring and Expo buffer. Afterwards, the action slammed home very easily.

I will take the hydraulic buffer with me back to the range for testing but am somewhat skeptical of it right now. The rifle is set for the next range visit at this point. Another Mil-Spec spring and buffer will be in the bag as well.


We have a ton of snow right now and I’ll have to wait to test my hypotheses. I expect that with the above changes, the two Beowulfs will run very well now.

I hope this helps you out!

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

A New .50 Beowulf Magazine Option: Lancers With Tromix Followers

I’m still experimenting with my .50 Beowulf (12.7x42mm) rifle and pistol that I have posted about previously. I wanted to find better magazine options – both in terms of looks and reliability – than my modified D&H aluminum magazines. I tried a number of different options and then happened on using Tromix followers in Lancer L5 Advanced Warfighters Magazines (AWM).

Tromix Followers

A small cottage industry has popped up of people 3D printing followers to center the various big bore cartridges in a given model of magazine. I’m still tinkering with some of the 3D printed models but during my surfing, I came across a machined aluminum model from Tromix Lead Delivery Systems. Tony Rumore and his colleagues at Tromix specialize in the .458 SOCOM round but they came up with a really slick follower design that would work with the really slick Lancer hybrid AWM Magazines.

I ordered in a few for testing and they are really nice. Here are a number of views for you:

Lancer Hybrid L5 AWM Magazines

So the above Tromix followers are made specifically to work with Lancer L5 5.56/.223 AWM magazines. The AWM considered a hybrid design because the feed lips are steel The lips can be a weak point in the design of some polymer magazines.

At any rate, the AWMs are really nice. You have a bunch of colors and capacities and are a very nicely made. They also have a number of capacities *but* for the Beowulf, stick to the 10 or 20 round magazines. The Tromix follower is relatively tall and can’t negotiate the curve in the 30s. It can be made to work with the 20s and I’ll detail that more in a moment. I have some thoughts on how to modify the Tromix follower to get it to work in a 30 but haven’t had the time to tinker with it yet.

The 10 round 5.56/.223 magazines can hold 3 Beowulf rounds without any tuning. The slight curve to the 20 round magazines can cause the follower to jam and we’ll cover how to address that next.

Tuning and Installing the Follower

Push the the button on the bottom of the follower and slide the base plate off. Note, the magazine spring will want shoot out so just be prepared to control the spring’s expansion.

This is an original Lancer follower stull attached to the spring. It’s really hard to get the assembly oriented wrong due to the design. The follower can only go into the magazine body one way. and the spring can only attach to the follower one way.
The spring can only fit into the Tromix follower one way also.
You then slide the assembly back into the magazine and slide the base plate back on. It is that easy.

The tuning required has to do with making the follower slide as easily as possible in the 20 round magazine. If you don’t then you are going to find that the Tromix follower jams inside vs. reliably pushing the cartridges upwards the way it should.

Now whether you do it before you install the spring or after, use a buffer and go all around the Tromix follower and make it nice and smooth. I used a 6″ buffing wheel with buffing compound. The reason I said you could either do it before or after is that I had already assembled four magazines before I realized I needed to do the polishing. Just rub off any buffing compound left behind. You’ll notice that the follower surface is far smoother to the touch than before.

I have used this 6″ Harbor Freight buffer a ton over the years as you can probably tell from the photo. It’s what I used along with some black/emory buffing compound to polish the followers.

The next step is to apply three coats of Teflon to the follower and the inside of the magazine body. I’d recommend using a dry lubricant inside a magazine body so it doesn’t attract dirt the way a liquid or grease would.

My preferred lubricant for inside a magazine body is Dupont’s Non-Stick Dry Film. It sprays on wet and leaves a layer of Teflon as the solvent evaporates off. Be sure to shake the bottle before spraying so the Teflon is floating in the can when you spray.

The trick I do is to use a heat gun to warm up the parts before I spray and then hit it with the spray lightly. I then warm it up again, let all of the solvent evaporate and then repeat for a total of three coats. I’ve hard far better luck getting a consistent thick layer of Teflon this way vs. trying to do it all in one spray.

The white dull look you see is the Teflon residue that will enable the follower to slide easier in the magazine body.

I spray the inside of the magazine body and all sides of the follower. Your goal is or there to be Teflon where ever the follower males contact with the magazine body. When everything is dry, reassemble each magazine.

Coat all four walls of the inside of the magazine body as well.


One quick comment – I do not recommend testing with live ammo. There are just too many things that can go wrong. I use A-Zoom 50 Beowulf Snap Caps to do my testing. They come in packs of two and I’d recommend having 4-8 rounds total for testing. Ideally, you’d like to load the whole mag you want to test so it really depends on what you plan on testing.

Get yourself 4-8 Snap Caps for testing. They are far safer than live rounds and hold up very well.

The Result

With the Tromix followers, the L5 AWM 10-round mags can hold three Beowulf rounds and the 20-round mags can hold seven. They are far, far more reliable than what I have been trying thus far.

The 10-round L5 AWM is on the bottom and the 20-round model is on top. You can see the big Beowulf rounds loaded to the capacity of each.
The weapon used first is this 7.5″ Beowulf pistol. Yeah, it bucks but I am trying to figure out the brake to use. There is a massive amount of unburned powder blowing out that pepper pot helical brake.
Target from 50 feet – rapid fire free hand. Yeah – feeding is way, way better.

The bottom line is that I am very happy with the pairing of the Tromix big bore follower with the Lancer L5 AWM 10- and 20-round magazines. I’ll experiment more to see if I can get the 30-round L5 AWMs to work but that is for another day.

I hope this helps.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

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!

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

Building a 12.7×42 (.50 Beowulf) 7.5″ Pistol – The Wulferine: Post 2 – The Forward Assist, Ejection Port Cover and First Look At The Barrel

In the last post, I gave an overview of the project and parts used. Rather than cover a lot of stuff again, here’s a link to my series of posts on building an AR Lower and rest of this post will be my covering the building of the 12.7×42 upper.

Stripped Upper Receiver

A Beowulf uses a standard AR upper receiver with an enlarged ejection port. My Alexander Arms (AA) upper has an ejection port that measures 3.02″ wide x 0.62″ tall. In case you are wondering, I grabbed on of my PSA 5.56×45 ARs and its port measures 3.02″ wide x 0.49″ tall.

The PSA’s port is about 0.35″ from the bottom of the base of the picatinny rail that has a casting line in receiver to the inside of the port. The AA still has the stepped lip for the ejection port door even though it doesn’t use one so I am measuring to the actual opening. I’m not sure how standard that measure is but offer it up – it does correspond with the top of the case deflector in the three ARs I looked at. The AA’s port is also about 0.35″. Note, this is an approximate. I’m trying to use caliper to measure a curved surface.

So this means you can either buy a standard upper and enlarge the port yourself or you can buy an upper that comes with the port already enlarged. Satern makes a big bore upper that supports the Beowulf round. Rather that bothering machining an existing upper, I went with the Satern receiver.

This is Satern’s stripped upper. They offer other options as well.

The Satern’s opening is 3.02″ wide x 0.62″ also. The slight difference is the measure from that casting mark under the rail to the entrance – it’s about 0.38″. Again – that last measure is a ballpark depending on the angle I hold the calipers. I can tell you for sure that it slight further down than the AA’s port.

A picture helps you compare. The top AR rifle is based on an Alexander Arms .50 Beowulf 16″ DIY Upper. The middle rifle uses the Satern Big Bore upper and other parts. The bottom is my 5.56 16″ PSA upper.

So, to assemble the base components on a stripped upper is easy. I’ll go cover each of the basic parts to make a complete upper.

Install the Forward Assist

It’s interesting when you read about the history of forward assists on the M16. Eugene Stoner, the original designer of the M16 platform, did not think one a forward assist (FA) was needed and that if one had to force the bolt to close then it would probably cause a problem later when it came time to extract. Colt, however, wanted to make government buyers happy. The US Air Force didn’t think the FA was needed but the Army demanded it have one and later claimed it was for psychological reasons.

I have a mixed opinion on them as do many people. If you must force the bolt closed then something is wrong. I’ve used it relatively little and there was, in all cases, underlying problems *but* it might help you fire that one round that makes a difference. So, I build with them, they are there but I very rarely use them.

This is a basic forward assist. It’s only 5 parts – the pawl (the part sticking out), a pin that holds the pawl in the body of the FA plunger, a spring and then the cross-pin to hold it in place in the receiver. The CMMG unit comes with the pawl and pin already installed. See how the pawl is shaped at the top in this photo? That’s the part that must be rotated to properly engage the teeth in the side of bolt when the FA is pressed.

With that said, the Satern upper has a provision for a FA and you need to install one. I used a model from CMMG and installation is easy:

  1. Lightly greased it first with Superlub grease and then inserted the assembly in into the hole with the pawl (the little “foot”) rotated towards the bolt.
  2. Press the FA all of the way into the tube and while holding the FA all the way forward, use a roll pin starter punch to drive in the roll pin that will hold it in place.

    Note, have some wood or something under the tube that the FA is going into. Supporting it will make driving the roll pin into place much easier. The starter punch gets the pin into the hole and then the standard roll pin punch will help you tap it into place until flush. It does not require a ton of force.
  3. Test the FA – it should spring in and out.
  4. Turn the receiver upside down and press the FA button again, you should see the pawl come out of it’s tube in the side of the receiver – it should be oriented/rotated to push on the “teeth” on the side of the bolt (yeah, that’s what those “ribs” in the side of the bolt are for.
If you want to make your roll pin work way, way easier, then invest in a set of roll pin starter punches and a set of standard roll pin punches. The punch on the left is a standard roll pin punch. The dome in the middle helps hold the roll pin in place and centers the punch on the pin. The punch of the right is for starting roll pins. The roll pin is inserted into the hole and supports the pin while you tap it in place. Both of these types of punches are extremely helpful.
It’s installed.

Installing the Ejection Port Cover Assembly

As you read above, the Beowulf has an enlarged ejection port so a standard-sized 5.56 ejection port cover/door will not work. Okay, you have two options at this point. Either skip the cover or buy one. I went with the latter because Satern makes an enlarged cover that fits their receiver.

The Satern comes with the cover, pin, snap ring for the pin and the cover spring. In my case, the clip was already installed on the pin as shown above.

In terms of installation order, installing the cover does need to be done before the barrel locking nut because the nut will block installation later. Here are the steps:

  1. If the clip hasn’t been installed on the pin yet, you need to tap it on square with a small hammer. I’ve had guys tell me they’ve used pliers for this step but I haven’t done that. Note, be careful and pay attention – the little clip can really fly away if it isn’t tapped into place squarely.
  2. Lay the upper receiver down with the ejection port up. I usually place it such that the barrel nut threads are to the right.
  3. Note the spring has a long and a short leg. The long leg will rest on the cover and the sort leg will rest on the receiver.
  4. The basic installation is to move the cover into place, slide the pin in from the left (back of the receiver) towards the right and sliding through the tube in the cover but stop just before the opening where you will put the spring.
  5. Note the spring has a long and a short leg. The long leg will rest on the cover and the sort leg will rest on the receiver.
  6. This is the part that drives me nuts – I pivot the pin away from the receiver just enough to install the spring. The short leg of the screw will go against the receiver and you need to twist the long end to create the tension.
  7. I then try and hold it all in place while sliding the pin the rest of the way in. There are videos out there on this and different people do it different ways. It can be frustrating so just be patient.
  8. Yes, the right end of the pin is just sticking out because once you install the barrel nut, it’s not going anywhere.
  9. You should be able to put a finger in from the bottom of the receiver well and pop it open. I do this as a quick test.
  10. To actually function test the cover, temporarily install the charging handle and bolt. Close the cover with the bolt closed as well. When you pull the charging handle back, the cover should spring open. If it does not, then you have most likely installed the spring wrong.
  11. Last step is to use some clippers and trim the small portion of the small leg of the spring that is sticking into the ejection port to get it out the way. Don’t do this until after you have the cover installed and tested.
Here’s the installed ejection port cover up close. The pin was slid in from left to right. You can see the short leg of the cover spring is to the left against the receiver and the long leg is to the right. When you install the pin through the spring, stop part way and angle it so you can twist the long leg around. Then, hold it together, angle the pin back down and slide it the rest of the way through. It’s an unnatural act and takes some practice. Test the cover and once it works, use nippers to trim that small bit of spring that is sticking into the ejection port.

The Barrel

In my opinion, you’ve just finished the hardest parts of the upper. I hate that little demonic dust cover spring just to be clear 🙂 The next three are pretty much tackled together because aftermarket handguards come with their own barrel but that needs to be installed.

First off, I went with Satern because the barrel in my first 12.7×42 rifle was made by them and was very accurate. Second, I liked that they sold it with a matching headspaced bolt. My biggest problem with my first rifle was that Radical Firearms did not include the right bolt. [Click here for my post about that first build if you are interested.] A common misconception is that a 12.7×42/Beowulf cartridge uses a 7.62×39 bolt. This is not correct. The depth and extractor are different. 6.5 Grendel does use the same bolt as 12.7×42. So, when I bought my Satern barrel, I bought it with a matching bolt just to play it safe.

Satern not only shipped fast but they packed everything really, really well. here you can see the 7.5″ barrel with the black protective cover on the threads and the yellow cap is holding the matching bolt securely in place. You can also see the gas port towards the middle and the indexing pin in the notch of the yellow cover.
The barrel is threaded 3/4-24. This is not the same as an Alexander Arms barrel. I asked Satern why and they told me they wanted a thicker wall. Whatever the reason, you need to remember this thread size when you are buying whatever brake or muzzle device you plan.

One of the really cool design aspects of the AR system is that the barrel just slides into the receiver and is properly indexed by the pin shown above fitting into a corresponding notch in the upper receiver. The barrel is “locked” into place via a barrel nut. A gas tube then slides into place over the barrel with the gas tube entering the upper receiver above the locking at the top. I’ll come back to that shortly.

This is just a mockup as the barrel nut has not been pulled out of the MI Combat rail yet. I will often do test fits to avoid surprises and make sure things are going to look the way I want them to – for example, I wanted to confirm the brake’s exhaust ports would clear the MI 7″ Combat Rail and they did. I also had planned to finish the barrel and brake a satin black Molyresin finish but was so taken with the stainless look that I changed my mind.

In Conclusion

After test fitting, it’s time to get into the installation of the barrel, nut, gas tube, handguards and brake. I’d say that’s enough to cover in the next post!

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

Building a 12.7×42 (.50 Beowulf) 7.5″ Pistol – The Wulferine: Post 1 – Planning The Parts

My friends know I am eccentric so I’ll point that out right up front. I design and build firearms that are very practical and some that are pushing the fringe. I’ve liked the .50 Beowulf cartridge (also known by it’s metric designation as 12.7x42mm). Bill Alexander designed the Beowulf to operate out a fairly standard AR platform which included a 16″ barrel and normal buffer. With the huge popularity of AR pistols with braces, I got to thinking – how short can I go?

Well, there are a number of pistol length uppers now that are 12″. Alexander Arms themselves both a 12″ complete upper as well as a 12″ DIY upper waiting for you to add your handguards of choice. There are cheap builders out there and I would tell you to be very careful to research the vendor before you buy. Some of them have awful track records.

Know what? I wanted to go even shorter and I had no problem buying the parts and building one myself. You see, I wanted a howitzer. To me, a howitzer is a firearm with a barrel so short that it can’t burn all the powder before the bullet exits resulting in a spectacular flare. Useful? Not really. Cool? Oh hell, yes 🙂

Satern’s Liberty Barrels & Upper Parts

If there’s one thing I have learned about the Beowulf, you need the right combination of parts or reliability will suffer. So that really meant that I needed to go with a reputable vendor. There’s a barrel company that really knows their stuff that you may not of heard about – Satern. They are located in Estherville, Iowa, and operated by Debra and Steven Satern. I talked to Deb a few times while I was planning my build. They were great to deal with and shipped fast – even with all the COVID craziness these days.

This is Satern’s stripped big bore upper that will work with 12.7×42 (.50 Beowulf), 450 Bushmaster and .458 SOCOM. The ejection port has been enlarged for the bigger cartridges. Note, they also offer a complete upper with the ejection port cover, forward assist, charging handle and bolt options as well as a complete upper without the bolt.

Satern has pretty much everything you will need to build a 12.7×42 upper. They have:

  • different barrel lengths – 7.5, 10.5, 14.5 and 16″ – note they come with the correct headspaced bolt. This is a big deal. Not all vendors use the right bolt and that causes reliability problems. Also, the thread is unique – 3/4-24 and not the 49/64-20 that Alexander Arms uses. This means you will need to either get your brake from Satern, Timber Creek or another vendor that supports a .50 cal with 3/4-24 threads. I went with Satern’s Heliport brake in part due to this threading.
  • They offer Barrel kits with brakes
  • Big bore forged uppers – basically a standard AR upper with the ejection port milled open larger. They offer uppers with the dust cover already installed or just a stripped upper
  • Gas tube assemblies

I went down their menu and bought the 7.5″ barrel, 3/4-24 Heliport brake, stripped upper, ejection port door, and pistol length gas tube from them. I just like doing my own thing is what it boils down to.

Other Parts

Once I had the main parts of the upper figured out, the rest was pretty easy. The lower is how-ever you want to build your lower. I planned for a pistol build using some of my favorite parts:

  • SBTactical’s SBA4 brace – it has six positions and the rear end is stiffer and better formed than the SBA3.
  • 12/28/2020: I am tinkering with the combination of buffer and buffer spring. Click here for a post about them.
  • Midwest Industries Combat Rail – these are very well made and finished. I especially like how the handguard fits onto their locking nut allowing for a ton of flexibility.
  • Vortex Strikefire II Red/Green Dot – these have a real nice wide field of view allowing for rapid target acquisition plus it can co-witness with iron sights out of the box.
  • BCM’s Gunfighter Mod 3B charging handle – I’ve become very fond if these over the year’s and the enlarged latch handle just feels right to me.


That’s it for now. The next post will start to get into the actual build.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

What is the 12.7x42mm cartridge? Is it the same as .50 Beowulf?

The short answer is that they are the same thing. The bullet’s diameter is 0.50″ which is 12.7mm and the case length is 1.65″ or 42mm. The reason you see some vendors say they have something to sell in 12.7x42mm is they are trying to avoid a trademark problem with Alexander Arms.

Bill Alexander, of Alexander Arms, did all the engineering to bring to life both the round and the AR components to use it. He also trademarked the term “.50 Beowulf”. As such, anybody who wants to sell something and refers to it as being for .50 Beowulf would need to get the permission and/or license the use of the term “.50 Beowulf” to avoid legal problems. So, a lot of vendors use the generic metric designation of 12.7×42 to avoid legal hassles.

With that said, bear in mind that not all engineering is equal. I have never had a problem with Alexander Arms parts but myself and others have had plenty of headaches with 12.7×42 components from budget AR vendors who haven’t done the engineering so buyer beware and research a vendor and their offering before you buy plus make sure they are reputable in general in case you need support.


So, short post this time. 12.7×42 and .50 Beowulf are the same round with different descriptions but be cautious to check out vendors selling parts using the metric designation. Some of them are selling junk so search for current reviews of products before you buy them.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

Looking for a Cool AR Rifle Project? Build a .50 Beowulf

Interest in the Beowulf round is growing as people buy the low cost 12.7×42 chambered pistols, rifles and kits. 12.7×42 is the metric designation for the Beowulf and is being used by groups wanting to avoid a trademark problem with Alexander Arms.

The Beowulf is one heck of a thumper delivering massive kinetic energy on target from the base AR-15 platform. That’s the remarkable part – it uses a standard AR lower! To give you an idea of the size of the round take a look at this photo. From top to bottom: .50 Beowulf 350gr XTP, 5.56×45 55gr FMJ , 7.62×39 123gr FMJ and a loose 9mm 124gr Hornady HST. The Beowulf sure dwarfs the little 5.56×45 round!

I’ve owned two .50 Beowulf’s and my current one was built using an Alexander Arms DIY kit that allows you to add the handguard and brake that you want. They are built on standard AR lowers so if you have an AR today, it’s just a matter of adding an upper in this caliber or you can do a whole new dedicated build – it’s up to you. I’ve also done a number of posts about my builds in case you want to learn more – click here to see a list.

A Beowulf upper can mate to any in-spec AR lower. This is a Spike’s lower with an Ergo group, Magpul PRS III and Geissele trigger.

What caught my eye the other day and prompted me to write this post is that Primary Arms has noticed the growing interest in .50 Beowulf and is now carrying a variety of parts and ammunition. They have a lot of products in stock and they ship fast. I’ve placed a couple of orders with them for parts over the past month and they are still shipping stuff out either the same or next day – that’s remarkable given how busy the industry is right now.

To give you some examples of .50 Beowulf products that Primary Arms has currently, they have the Alexander Arms DIY 16″ barrel kit and also the Timber Creek Heart Breaker muzzle brake, which is my favorite Beowulf brake.

This is the 16″ DIY kit. Alexander Arms has done all the fitting for you. It comes with one magazine as well. In terms of the upper kit, I found the machining and parts fitment to be excellent.
This is the Timber Creek Heart Breaker and it does a remarkable job of reducing the recoil. It has three heart shaped ports on each side that redirect the blast backwards to propel the rifle forward and reduce recoil. The three circular ports on the top help reduce climb. Seriously, this is a solid brake.

For ammo, there is an increasing variety out there – Alexander Arms makes their own with a variety of loads plus there are other sellers out there with their own offerings. I’ve found the Alexander Arms 350 grain Hornady XTP ammo to be accurate and the XTPs really open up on impact.

The is older packaging. In 2019 I noticed Alexander was using an eye catching color scheme of navy, black and white – same ammo just a different box. The Alexander Arms .50 Beowulfl 350gr XTP ammo is packed 20 rounds to a box and Primary Arms has it in stock.
Here’s the whole Beowulf.

So, if you want a fun build, get the kit, the handguard you want, the brake you want and take it from there. For folks who like optics, I’d recommend something that can help with fast moving up close targets as well as out to about 200 yards — I paired mine up with a Vortex 1-6×24 Strike Eagle and the 1-8×24 model would be great also.

This is my 1-6×24 Vortex Strike Eagle using a Vortex cantilever mount on my current Beowulf rifle.

One last comment, I make my own magazines using the reliable but inexpensive aluminum D&H magazines that PSA sells. They typically go for $9.99 on sale to $12.99 normally and right now they are on sale in case you want to snag some – they also have their special going on where you can get one of their 36″ rifle cases plus 7 D&H magazines for $109.99

This is one of the 30 round D&H 5.56 magazines that you can use to hold up to 10 Beowulf rounds.
This is the very well made 36″ PSA rifle case deal that includes 7 D&H mags.


That’s it for now. I hope you found this helpful and have fun building and shooting a .50 Beowulf.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.

My Favorite .50 Beowulf Muzzle Brake

I now have built my second Beowulf and guys ask me about the recoil all the time – the short answer is that it’s very manageable. With just a bit of tuning, I’d put it somewhere between a 20 and a 12 gauge shotgun shooting 2-3/4″ magnum loads. Now that there are a ton of options both from Alexander Arms as well as generic 12.7×42 uppers (the metric designation for the Beowulf so they don’t have to pay royalties to Alexander Arms), a lot of guys are getting into the .50 Beowulf cartridge and ask me about what brake to run with.

My favorite is the Timber Creek Heartbreaker. It does a remarkable job of venting gasses backwards to compensate for the recoil it would otherwise have. I liked it so much on my first build that it was what I used in my second build. It’s very affordable and I’d be surprised if you can find a brake that does a better job!

Side view of the Heartbreaker and you can see where it gets its name.
View from the top. Note the brake includes a jam nut.

Finding The Brake

My first recommendation is to check out Primary Arms – they carry them and ship fast.

The second option is to buy the brake from is eBay. Just make sure that the thread of the brake matches the thread on your barrel because there are two different threads floating around out there.

My Alpha Wulf

I did a series of blog posts when I built my second rifle. My pet name for it was the “Alpha Wulf” or the leader of the pack. It’s all premium parts and probably my best AR build when it comes to paying careful attention to details during assembly. Here are the posts:

I’m a big fan of the .50 Beowulf cartridge and hope you find this post helpful!

Note, I have to buy all of my parts – nothing here was paid for by sponsors, etc. I do make a small amount if you click on an ad and buy something but that is it. You’re getting my real opinion on stuff.

If you find this post useful, please share the link on Facebook, with your friends, etc. Your support is much appreciated and if you have any feedback, please email me at Please note that for links to other websites, I may be paid via an affiliate program such as Avantlink, Impact, Amazon and eBay.