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.458 SOCOM is one of the most potent rounds that will fit in the AR-15 platform, but factory-complete rifles (or even just uppers) are scarce. Identifying what I believe is an upwards trend in the caliber’s popularity, CMMG has hit the market with a unique rifle designed specifically around the .458. It’s an AR-15/AR-10 hybrid, and it’s called the ANVIL.

For those who aren’t familiar, .458 SOCOM is a highly adaptable and useful caliber for everything from hunting to home defense to detonating fruits and veggies in fantastic fashion. Likely its most popular use is in the hunting of feral hogs and wild boar, where its 2,500+ ft-lbs of energy really knocks ’em flat. But, with supersonic and subsonic loads ranging in projectile weight from 140 grains to a whopping 600 grains and in all manner of composition and design, it’s very versatile.

Left-to-right in the photo above, loads are as follows: 500 gr JSP Subsonic, 140 gr ARX, 300 gr Solid Brass, 300 gr JHP, 300 gr Lehigh Controlled Fracturing, 300 gr Lehigh Xtreme Penetrator, 350 gr FMJ Subsonic. Manufacturers represented are SBR Ammo, Underwood Ammo, and Detroit Ammo Co.

The chubby .458 SOCOM single stacks in a standard AR-15 magazine. What’s normally a 30-round mag when filled with .223/5.56 fits 10 rounds of .458. A 20-round AR mag will hold seven. CMMG’s ANVIL ships with what I think is the best AR magazine on the market, a Lancer L5AWM, which will actually hold 11 of these big slugs if pressed.

A proper .458 SOCOM upper contains a barrel extension with a modified feed ramp. Those M4 cuts just aren’t suited to the fat, centered-in-the-feed-lips cartridges, and the preferred solution is hogging the dual ramps out into a single, wide ramp that’s blended into the receiver itself. The ANVIL’s isn’t the prettiest I’ve seen, but it does the trick.

The ~0.54-inch thick cases won’t fit through a standard AR-15 ejection port, so this has to be hogged out on most uppers as well. In the case of the ANVIL, though, the ejection port is oversized from the get-go. Actually, the whole upper is oversized…

Most companies run a bored-out bolt face to accommodate the .458 SOCOM’s 0.473-inch rim diameter (same size as a .308 Winchester and many other full-power rifle cartridges), but this leaves precious little material under the bolt lugs and greatly increases the likelihood of breakages. Likely enough, in fact, that I’ve witnessed it happen twice, once on a .458 (at Texas Firearms Festival) and once on a 7.62×39 AR upper despite that caliber’s smaller, 0.447-inch rim diameter and ~1,000 ft-lbs less power.

So this is where the hybrid AR-15/AR-10 design of the ANVIL comes in. The bolt carrier group seen above is a .308 Win design, as used in CMMG’s Mk3 series of rifles.

If you tried to stuff it into a standard AR-15 upper receiver…well…see above. The carrier is much too wide to fit. Likewise, the bolt itself is larger in diameter, allowing extra meat under the locking lugs, and the same applies to the barrel extension.

It’s basically an AR-10 upper (pins about a half inch farther apart than the AR-15)…

But the lower doesn’t extend as far behind the grip as on an AR-10/SR-25 lower, and obviously the magazine well is designed to accept AR-15 STANAG mags. In the pic above, the ANVIL lower is on top and an AR-15 lower is seen below it.

Bottom line: it is, indeed, a hybrid. While this does mean a bit more size and weight than a true AR-15, that extra meat on the bolt is comforting and it’s still smaller than a full-on AR-10.

A Magpul CTR Stock rides on a 6-position, mil-spec receiver extension. The ANVIL also sports a Magpul MOE pistol grip.

Under the CMMG handguard, which features a full-length Pic rail up top and KeyMod points along the 3:00, 6:00, and 9:00 sides, is a 16.1″ barrel made from 416SS with a 1:14″ twist. It runs a carbine-length gas system with a very nice, adjustable gas block from SLR.

At the end of the 5/8-32-threaded barrel is a big-bore version of CMMG’s SV Brake.

Before they can exit via that brake, though, bullets — loaded in a case, loaded in a magazine — first go in the generously oversized magazine well. Despite my obvious attempts, it’s hard to miss this thing!

Standard safety lever, dimpled take-down and pivot pins, standard charging handle. The billet lower has an integrated trigger guard.

The trigger is CMMG’s single stage mil-spec style trigger. It’s pretty much what you expect from mil-spec/parts kit, except for a lighter-than-the-norm 6-lb pull. If you go with the XBE2 model — $200 more — instead, it ships with a Geissele SSA trigger.

I was a little worried when I got my beat up loaner ANVIL, as it had clearly fired a decent number of rounds through it and the gas rings were basically shot. They’re loose enough inside of the chrome-lined BCG that the bolt drops right down into it under its own weight — practically no resistance at all.

However, the rifle ran great. Firing that full spectrum of ammo weights and power levels, including some suppressed shooting with my Liberty Cosmic on the end, function was 100%. It fed smoothly and ejected consistently.

Feeling it was a bit over-gassed as it arrived, I dialed down the SLR block a bit and could tell the buffer was no longer impacting the rear of the receiver extension with such reckless abandon. This could explain some of the gas ring degradation, though on that note CMMG informed me at the NRA Show that they just upgraded to a higher grade of gas ring that will outlast the current ones.

You’d never mistake the recoil for a 5.56. There’s just no getting around the fact that you’re sending a projectile with 5-10 times more mass downrange at speeds fast enough to net about twice the muzzle energy of the cute little 5.56 pill.

It’s a thumper, but thanks in a big part to the AR-15’s gas impingement system and in-line recoil setup, it’s controllable and isn’t uncomfortable. That said, I shot about half of my testing rounds through the ANVIL with the Adaptive Tactical EX Performance Stock installed, and the difference was welcome.

Accuracy for me was a bit of a mixed bag depending on the ammo. Shooting 3-round groups, it ranged from a tight 1.45 MOA with the Detroit Ammo Co 350 gr subsonic up to 4.32 MOA, with the norm coming in a bit over 2 MOA. Frankly, I probably could have snugged up these 100-yards groups a bit if I were shooting a scope with more zoom than the 1.5-6x US Optics SR-6S, so I think it’s fair to say it’s a 2-MOA gun with many ammo choices and somewhere around 1 MOA with ammo it likes.

Aside from finding a load the gun likes and knowing what sort of accuracy you can expect from it, you’ll want to take note of point of impact. Considering the huge variation in bullet weights and velocities, POI shift is meaningful load-to-load. Most moved up or down predictably based on velocity, but there was some left/right shift to account for as well.

While the .458 SOCOM is considered a close-range caliber, with the 2 MOA-or-better loads I’d be very confident hunting hogs inside of 150 yards and, with proper DOPE, out to maybe 250. Confirming that theory on the range, I dialed up the hold for 250 yards and rang a steel gong and silhouette with boring consistency through two mags of two different loads.

Through 200 rounds — and you’ll have to excuse the lower-than-usual testing round count; this stuff ain’t cheap — I had two of what I’ll chalk up to user-induced issues. AR mags are really designed to double stack, with any given round fully to one side and under just one feed lip. As the .458 runs single-stack, it’s possible to accidently push the back of the top round through the opening in the spine of the magazine just under the feed lips.

It won’t go through without some extra effort to “pop” it across, but I managed to do it twice before I took note and stopped shoving them back so hard. As different magazine brands and models have different sized and shaped openings there, I’m sure some wouldn’t allow this issue and some might be worse. Something to be aware of, at any rate.

Whether for hogs, dangerous game, or other dangerous threats, the versatile .458 SOCOM offers significant firepower in an AR package. While the caliber will actually fit in a standard AR-15, CMMG has made a wise decision with the creation of its hybrid ANVIL. The larger, heavier BCG and bigger bolt head with stronger lugs is better suited to long-term durability.

After all, a gun chambered in .458 is likely one you’ll want to be able to count on.

Specifications: CMMG MkW-15 XBE, .458 SOCOM, SBN, ANVIL

Caliber:  .458 SOCOM
Capacity:  10 rounds in most standard AR-15 magazines
Action:  Direct gas impingement w/ carbine-length gas system. SLR adjustable gas block.
Length:  33.5″ with stock collapsed
Weight:  7.5 lbs unloaded
Barrel:  16.1″, 1:14 twist, medium taper, 416SS, salt bath nitride, threaded 5/8-32 w/ CMMG SV Brake
Receivers:  Billet 7075-T6 aluminum hard-coat anodized. CMMG mid-size MUTANT hybrid platform
Furniture:  Magpul MOE grip, Magpul CTR carbine stock, CMMG RKM15 handguard
Trigger:  CMMG single stage Mil-Spec style
MSRP:  $1,949.95

Ratings (out of five stars):

Accuracy: * * *
Three stars is average and that’s solidly where this rifle is for a .458 SOCOM. With a load it likes, a higher zoom on the scope, and maybe a nicer trigger I have no doubt it’ll lay down 1 MOA or better groups. For hunting hogs inside of 150 yards, it’s a-okay.

Ergonomics: * * * * 
It’s an AR. Though I did prefer the Adaptive Tactical stock on this gun.

Reliability: * * * * *
Worn out gas rings be damned, it ran smoothly in every way.

Customize This: * * * * *
It’s an AR. In 30 seconds I had a different stock on it. In one minute I had a suppressor on it. In a few minutes of tinkering I had the gas system adjusted more to my liking. It has KeyMod points all over the handguard.

Overall: * * * *
The ANVIL is a well-sorted .458 SOCOM carbine. It’s bigger than an AR needs to be for the caliber, but it’s as big as an AR really should be for the caliber. The adjustable gas block is a very nice upgrade that could have easily been overlooked, though with the large variation in available loads and the popularity of suppressing the .458, it was absolutely the right choice. A full-length rail opens up more options for night vision-equipped hog eradication. Fit and finish are quite nice. Overall, it’s a solid gun and a strong performer.

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  1. i have a friend with this company’s mutant hybrid. it has a bigger bolt for the 7.62x39mm round and runs like a tank.
    they do beefy.

  2. That looks like a super nice rifle quite impressed you go cmmg. I built my rifle from regular AR-15 receivers however I had Tony over at tromix set me up with all the parts I needed and I’m using a Daniel young manufacturing bolt carrier group specially designed for the 458 Socom and I have had absolutely no issues out of 1400 rounds through the rifle now. This thing shoots 1 MOA at 160 yards no problem 16 inch stainless steel barrel I’m using Lancer mags that Tony at tromix modifies a little bit the very front of the magazine he puts a little dimple cut out so that the 458 Socom rounds in the heavier grain bullets like the 4/5 and 600 grain bullets can clear the magazine without an issue. But I absolutely love my 458 Socom it’s probably the rifle I shoot the most out of all 20 AR Zone thanks again tromix you guys are great company.

  3. Zero style points. CMMG seems to be coming out with some AR products with a slight twist. Good for them.

  4. So this is “The Truth about Guns” right?

    “but factory-complete rifles (or even just uppers) are scarce.” – Baloney, you can get on Tromix’ website and have one at your house in a couple days depending on how much shipping you want to pay.

    “Likely enough, in fact, that I’ve witnessed it happen twice, once on a .458 (at Texas Firearms Festival) and once on a 7.62×39 AR upper despite that caliber’s smaller, 0.447-inch rim diameter and ~1,000 ft-lbs less power.” – Was this a Tromix 458 bolt, or one of the ripoffs out there that use substandard components?

    Im happy that CMMG, who generally makes pretty decent stuff, is pushing this caliber. Its a beast, like shooting a semi-auto 45-70. What I am not happy about is that they ripped off the chamber reamer design from the actual owners, Tromix and pass it off as their own. 458 SOCOM is not SAAMI approved yet, thus the reamer design is actually proprietary. So every company that sells a 458 SOCOM chambered rifle that doesnt actually use the correct reamer is ripping someone off. Also, CMMG says that the bolts that are in use for 458 are not strong enough? There are multiple guys that have run their bolts into the 10,000 round mark with no failure yet. CMMG also went on the 458 SOCOM forums that are run by Tromix and crowed about this and that, and while the community over there is generally very accepting and helpful, the CMMG rep got hammered because it was brought to light that CMMG was ripping off Tromix using unapproved reamers and saying that their guns are “far” superior to anything anyone else has out there. What do you think the actual reception of that was? Any issues this caliber has had in the past can be summed up in a single sentence: Any of the rifles that had issues were not approved for manufacture by Tromix and were likely using an bastardized reamer and sub-standard bolts and barrel extensions.

    I have no beef with CMMG, they generally make pretty good stuff, and I own a few parts and pieces for various guns made by them. But I call bullshit on this review. The author needs to get his facts straight instead of re-writing the CMMG literature for the review. Maybe you guys should call Tromix and get an upper from them? I can bet it will out shoot the CMMG all day.

    • I agree with you Tony over at tromix is a very nice guy and they’re good people over there. The problem is everybody tried to copy his design by reverse-engineering it and they came up short when doing it take rockriver for example with their 458 Socom project I hear nothing but complaints from about everyone that has ever owned one of those calibers in 458 rifle just does not cycle and function correctly. If you’re going to buy a 458 Socom why not buy it from the guy that helped design the cartridge and actually built the components to make the cartridge work in the AR-15 such as the barrel gas block and Bolt. It’s just my $0.10 worth but if I’m going to buy a 458 like I already had I’m going to buy the components and build it myself so that I know it’s built correctly and to my satisfaction and I’m going to buy the parts from the people who actually designed the cartridge and the weapons system to begin with OR the caliber to fire in the weapon system to begin with I should say. LOL

      • Wilson Combat had issues with some of their guns as well as they use a PTG reamer.

        Just kind of sucks. Tony and Marty designed a great cartridge, and they get crapped on because a bigger company decides that they want to rip off their idea.

        There is an authorized reamer usage list out there, but I cant seem to locate it at the moment.

    • Actually, Corey, I don’t think I was aware of that info. The history of this cartridge isn’t something I had researched. I reviewed the gun as its own thing without coloring the review with the political/historical info that you’ve brought up. I stand by everything in it as factual per my personal experience with this rifle. I didn’t speak with CMMG and the only info that comes from them are the stats (price, length, materials, etc).

      “but factory-complete rifles (or even just uppers) are scarce.”/
      By that I meant options and brands. How many companies can I buy a 5.56 rifle or upper or barrel from and in how many configs and styles? How many can I buy .458 versions from. Yeah.

      On the bolt lugs breaking thing, I don’t know what brands they were. 7.62×39 AR-15 bolts have earned a bad rep for it. I’ve witnessed one of those break, and I’ve witnessed a .458 S bolt break as well. It occurs to me that they can be prone to the same issues as the 7.62 bolts for the exact same reasons. If Tromix has done something cool to beef up the lugs that’s great. I didn’t mean to imply anything about that specific brand. But the truth stands…if you thin out the material holding the lugs to the bolt to practically nothing, you weaken them. CMMG went a different route. If Tromix went a different route also that’s amazing. This isn’t a Tromix review.

      FYI I’m building myself a suppressed .458 SBR upper right now. It’s looking like it’ll involve me purchasing mostly Tromix parts (spoke to them like two months ago about it). You’ll get your Tromix review, fan boy, you’ll get it…but it’ll be the truth as usual, so guard yourself just in case, snowflake… 😉

      • Jeremy:

        “How many can I buy .458 versions from. Yeah.” – Easy, really only Tromix, because they are pretty much the only game in town that is licensed to do it. There are only a handful of manufacturers that are allowed to use the 458 reamer, that part of the issue. If the cartridge would get SAAMI acceptance, then it would be less of an issue. Remember, technically we are still dealing with a wildcat here, even though its very well established and proven.

        The 7.62X39 bolt lugs break because they arent strong enough. The Tromix ones do not as they are not the same design and are made from better material. The CCMG bolts are physically alot larger, as the BCG is AR10 sized as you have seen. Its not a bad design, but it defeats the purpose of being able to drop a different upper on a standard lower and shoot a different caliber with the same lower. If you have the CMMG still, take some accurate measurements of the bolt and compare them against the Tromix?

        Im in the same boat as you as I am in the process of building one. Ordered a spare M4E1 upper from Aero last week. Barrel will be ordered here sometime in the next month. I kicked around 450 Bushmaster and 50 Beo, but the big thing for as Im a handloader is the dearth of bullets available at 458 caliber. Not to mention, long brass life, good feeding, and no special mags.

        Im not saying the CMMG is a bad rifle. In fact, its great. Ive handled one. My only complaint is that its big and heavy. Every review Ive seen has been positive. And generally CMMG makes really good stuff.

        Fanboy? Hahaha, not really. Ive seen too many small companies great ideas get ripped off by bigger companies. CMMG did it with this rifle by short cutting getting getting approval for the reamer for the barrel, and then using the name as well. They should get their ass sued for patent and copyright infringement. Im kind of glad they arent though as that kind of shit backfires more often than not in this industry and can push away business from negative press.

        Snowflake… You so funny. 🙂

    • Tony Rumore (Tromix) only has the caliber licensed. He doesn’t own it. It is actually property of Teppo Jutsu.

      That said, his stuff rocks and I’ve been very happy with my 458 upper.

  5. Yeah I’m surprised they put a 6 position collapsible stock on this rifle. I haven’t seen it personally but I have been informed from a coupla guys that their collapsible stocks collapsed and broke from The Recoil that they experienced. This made me decide to run a rifle length receiver extension tube and a wolf XP rifle length spring with a standard rifle length AR-15 buffer which I believe is around 10 ounces. This gave me a lot more recoil reduction. The rifle is very manageable to shoot with this style setup I ran a regular Magpul Moe stock on it and it seems to digest whatever I put in it without an issue. And I’m also running young Manufacturing national match full Mass bolt carrier group that is like an ounce and a half heavier then a regular M16 bolt carrier group and it’s chrome-plated. In mr. Young and builds his bolts for the 458 Socom and he designs them in a way that I have actually heard from Tony over at tromix that he had a customer handloading 458 Socom rounds and blue the barrel extension lugs out using a young manufacturing bolt That’s How Strong they are they don’t fail.

  6. The problem is with all other Big Bore calibers except for the 375 Reaper they’re all straight walled pistol cartridges. The 458 Socom is one of two that actually have bottleneck rifle cartridges which make it feed a heck of a lot better than the 50 Beowulf the 450 Bushmaster.

    • Also, what he said.
      Although in a drum magazine (I’d buy *that* for a dollar!) a straight wall case might be preferable?

  7. I want a .458 simply because of the kudzu, short sightlines, and steep terrain that I have to deal with here when hunting pigs. They used to stick to the creek beds and dry washes, but in past years have started side-hilling. I’ve been walking the old swine superhighway, heard multiples up the hillsides, and caught glimpses of them through the vines.

    Really, the only way to get at them is to find an opening from below & shoot uphill (never a good idea), or find the entrance to a kudzu pig tunnel and set up there.

    Generally their trails are pretty straight, but I’ve watched even 7.62×39 get dragged off target by encroaching vines, resulting in sloppy kills. Shots presented are also often head-on, and similarly we’ve seen a couple rounds skip off a hog’s skull (usually knocking them out, but still….).

    The other option is 12ga slugs, but also in recent years its physically hard to handle my shotgun’s size & recoil (Mossberg 835 w/ a slug barrel).

    I’d much prefer a semiauto .45-70, but AFAIK there’s no such thing as a .45-70 AR. I have also considered the .50 Beowulf & .450 Bushmaster, but the .458 seems to have better availability, variety, & performance for my needs.

    • Yeah for me I’ve chosen to build a .458 due primarily to the reasons you mentioned: ammo availability, variety, and price compared to those other calibers. Plus suppressor options, which are more limited for the .50. I do like the super rebated rim of the Beowulf, though. But otherwise I suppose I prefer the necked design of the 458.

      • Maybe it’s just me being irrational, but I always felt like straight case rifle rounds are easier to damage/set back and kinda belong in lever/pump guns. Although if I was rolling my own, it’d probably be faster/easier to reload the straight cases(?)

        I always planned on putting a can on my PTR 308 first… but a .458 pretty much begs for one imho.

    • The main advantage of the .458 is that it uses .458 Rifle bullets and not .451 pistol bullets.

      Thus .458 SOCOM bullets have (in general) much heavier construction than the Bushmaster.

    • NW-ish Alabama, where neighbors don’t care if I set off 5lbs of tannerite on our back 40 (except before 2pm on Sundays). We’re surrounded by mines… So I got that going for me, which is nice.

      • Yeah brother I’m in Florida not too far away 458 is screaming to put some Hogs down LOL

  8. Too bad its keymod and me and the navy seals now agree that it must be shit.

  9. I’d say it’s pretty optimistic to call this a 1 MOA rifle. I thought the TTAG standard was 5 shot groups.

    With that being said, it’s an interesting rifle. I like the. 50 Beowulf better. Mine ran 2-4 MOA (AE Advanced 16″ upper over a CMMG lower with a mil spec trigger). I wound up selling mine for an AR-10.

    • I did 3-shot groups due to ammo expense and the fact that I had collected quite a few different loads and wanted to group most of them. Glad I did, because if I had only picked one or two I may have come to a different conclusion about its accuracy. This at least made it clear that this gun is a bit picky on ammo when it comes to group size (it ran all the loads flawlessly).

      You’re right on the MOA thing. I’m confident with a different scope and the load it liked I could shoot 1 MOA, 3-shot groups with consistency. As for what that would translate to for our standard, 5-shot groups? Hard to say for sure. This is also a sample size of one rifle, of course.

  10. There’s one serious drawback for this caliber. There is little published data. Everything from Teppo Jutsu (the caliber’s designer) is generated from QuickLoad. While it’s a great software with immense data, QuickLoad’s predictions are not a good means of developing start/max loads. The software even warns against this practice.

  11. One of the fellas that rights or the blog here knows quite a bit about 458 Socom and Tony over a Tromix can answer quite a bit a load data questions if you have any just give him a call he’s glad to help out he’s a very nice guy. Yeah I’d like to see this cartridge get approved so that we can actually have some load data it’s slowly starting to come out though I’m starting to see more books with 458 load data in it so that’s a plus. Hey Jeremy where are you located man? Are you in Texas it as well?

  12. Jeremy we should plan a hog hunt over on your side of the pond LOL I’m in Florida get a couple of the guys together and go do an nice hog hunt one weekend what do you say?

  13. Wait – since the Mags only take 10 rounds that must make it less deadler(er) . . . right ? My congressman told me so, they never lie.

  14. re: CMMG trigger. If anything I’ve found CMMG trigger kits to be a bit better than generic mil-spec. Not fancy, but smoother, lighter and crisper. I’ve built 3 ARs with them over the course of a few years and all were decent. I had thought the first one was a fluke.

  15. billet receiver is weaker than forged. SS barrel is brittle compared to CMV or even CroMo. bolt lugs are unsupported for 1/4 to 1/3 of the diameter. keymod breaks.

    no thanks

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