.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
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.