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3 Guns in One With CMMG Resolute Uppers

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It could be said without much argument that the AR-15 rifle is the most versatile and modular weapon system on the planet. A shooter can configure their rifle exactly how they want it with optics, furniture, and other accessories. An AR-15 can be configured as a rifle or a pistol — and there are even options for shotgunners too. Caliber choices run the gamut from 22 rimfire all the way up to a single-shot 50 BMG upper receiver, along with just about every conventional (and some not so conventional) rifle and pistol cartridge in between.

For any individual concerned about preparedness for any calamity, it makes sense to have at least one AR-15 on hand. And with a variety of upper receivers and the appropriate magazines, you can make that one rifle even more versatile.

Companies like CMMG have taken the guesswork out of converting from one caliber to another, offering a 22-caliber conversion kit and a variety of upper receivers in everyone’s favorite pistol caliber.

Magpul Magazine CMMG Logo
Make sure you use the correct magazine with the upper receiver in question.

They sent us 5.56 and 9mm Resolute series complete uppers to wring out. CMMG Resolute uppers are the higher-end options that CMMG offers and come with all the bells and whistles you’d expect.

You needn’t use a CMMG manufactured lower with these uppers. In fact, we reached out to them to ask for one of their lowers, but they insisted we run them on whatever lower we had on hand.

Challenge accepted!

Anderson Manufacturing

No stranger to the AR platform, yours truly has been shooting, building, and trying to destroy them since the 1980s. These CMMG uppers could easily run on a Colt, FN, Cobalt Kinetics, Mega, Bushmaster, Palmetto, or any number of others. Instead, we chose one that would make some snob shooters climb the walls — an Anderson Manufacturing lower receiver with a Vietnam-era CAR-15 stock would be our host gun.

Read any internet forum or social media group dedicated to the AR-15 and you’ll find plenty of users maligning Anderson and their products, calling them “Poverty Ponies.” Some will assure you that the rifle will grenade in your hands.

You could argue that bargain budgets invite builders who use substandard, cheap, or questionably made parts — that’s true of anything when it comes to a build. We put this one together when we had a TPS lower parts kit looking for a home and found the lower on sale for $30.

Anderson Lower
Make sure you use the correct magazine with the upper receiver in question.

There was absolutely nothing out of spec with the Anderson receiver; the lower parts kit installed and function checked perfectly, as did the replica Vietnam-era CAR-15 stock. At one time, this was going to form the foundation for a lightweight rifle build, but it had just been collecting dust in the safe ever since. So we decided to give it new life.

CMMG Resolute Upper in 5.56

The first and most important upper in CMMG’s system is the 5.56 NATO one. It featured a nice burnt-bronze finish, with an M-LOK-compatible rail system as well as CMMG’s fantastic ambidextrous charging handles, a mid-length gas system, and one of CMMG’s clever muzzle devices. It took less than a minute to pop the receiver pins open, and the upper was ready to go when they locked back into place.

For 5.56 magazines, we ran aluminum GI versions by Okay Industries branded as Sure Feed. They consistently perform well and are strongly reminiscent of the versions we used in the military. C-Products made many of those magazines back in the day, and all they’ve done over time is improve on their product.

CMMG Resolute Upper 9mm

Sometimes we get lazy and mount a set of MBUS sights on a rifle for testing, but this time we wanted to mount a Low Power Variable Optic (LPVO). We chose a Sun Optics USA Mantis 30mm 1-6×24 with an illuminated BDC reticle in a one-piece Weaver tactical mount. As a reformed optics snob, these scopes offer great clarity for the money.

An LPVO gives the shooter true 1x to shoot with zero magnification. It’s not as fast as a red dot or holographic sight, but it can be a very close second. LPVOs are typically adjustable in magnification up to a maximum power of 4 to 8, besides the handful of 1-10X scopes on the market. This gives the shooter the ability to increase their magnification for longer-distance shots and positive target identification.

The Mantis is a second focal plane scope, meaning the reticle size remains the same regardless of magnification. We zeroed at 200 yards and found the CMMG mounted on an Anderson lower with the SOUSA scope to be a sub-MOA rifle.

To be perfectly honest, with a good optic and a consistent upper, there’s very little that a rifle such as this can’t do. Granted, a bull moose might be off the menu, but there are other uppers to help you in that regard. 

9mm Upper

The second upper that we received from CMMG was a Resolute in 9mm; fortunately, it had a gray finish to distinguish one from the other. It’s helpful to be able to easily identify your uppers, especially when you’re switching calibers. Some folks etch the caliber on the ejection port cover or have it painted on the receiver. These are reasonable ideas, especially if you order all your uppers in the same color. 

AR 15 9mm magazine CMMG Resolute
The 9mm magazine uses a block in the front of the magazine to maintain the same profile as a 5.56 mag instead of a skinnier pistol or SMG magazine.

A while back, a major manufacturer shipped out a rifle for a review. At the same time, they sent a similar rifle to another writer. I got his, and he got mine. It was fortunate he phoned me, because the guns weren’t marked, and I would’ve inadvertently loaded 458 SOCOM into a 50 Beowulf.

While I’m not a huge fan of pistol-caliber carbines, they do serve a few purposes. They can be made quieter, ammunition can be cheaper, and certain ranges only allow pistol calibers. One of the problems is the magazines for which they’re designed to work. There’s no common standard — some take Glock extended magazines, others take Uzi or MP-5 magazines, and some take other pistol magazines. Shooters often make their choice based on the number and type of 9mm magazines they already have on hand.

The secondary problem can be finding appropriate magazine pouches, especially when mounting them on your plate carrier, combat harness, or war belt. Then, there’s the hassle of swapping them out, for instance, when you usually run 5.56, but need 9mm for a PCC match.

CMMG Resolute Upper 22 LR Conversion

CMMG offers a dedicated magazine made for this upper that has the overall look, feel, and footprint of a 5.56 Magpul P-Mag magazine. We loaded them up with Federal 115-grain FMJ and let a few hundred rounds rip downrange. 

For an optic, we ran a Nikon Spur red dot. This is a clear, robust fixed-power sight that’s roughly the size of an RMR. Between the lack of magnification and our aging eyes, we achieved about 2-inch groups at 100 feet. If you’re good with a 1x red dot, it’ll work fine; though in the future, we may dial it up with a low magnification scope.

CMMG 22LR Conversion Unit

If you’ve been shooting ARs for any length of time, you may be familiar with 22LR conversion kits for the AR platform. Simply remove your 5.56 bolt and replace it with a drop-in dedicated 22LR bolt. These kits take a proprietary magazine and give you two calibers in one unit.

We were ready to be disappointed, as these units can be very hit or miss with regard to reliability and accuracy — an AR typically has a higher twist rate than a 22LR barrel, and there’s about 1¾ inches of freebore in the chamber before the bullet stabilizes.

CMMG Resolute Uppers conversion

CMMG’s unit is completely made from stainless steel, which makes it easy to maintain and clean. As we all know, 22LR can be incredibly dirty to shoot.

The magazines that come with this kit resemble a typical GI magazine on the exterior, so they can easily fit in your existing magazine carriers. You can quickly tell the difference from standard 5.56 magazines, as they have visible rivets on the outside and the feed ramp noticeably protrudes from the top. They’re the best-looking magazines for any conversion kit or dedicated rimfire AR that we’ve seen.

To use the conversion kit, break open the rear of your upper receiver and remove the bolt carrier group and charging handle. Replace the 5.56 bolt carrier group with the conversion bolt, then reinsert it into the upper receiver with the original charging handle, close the receiver, and you’re ready to go plinking.

As it turned out, our groups impacted about 4 inches lower than with the 5.56 barrel; it was pretty consistent otherwise. A few boxes of 22LR turned into half a brick, as it was a blast to shoot. We experienced two failures to feed, but the blame lies squarely with the ammunition and not the rifle nor the conversion bolt.

22LR conversion CMMG Resolute Uppers

Typically, I recommend a dedicated 22 rimfire rifle and/or pistol for most survival or bug-out scenarios. Shooting the CMMG rimfire conversion bolt has me rethinking this a bit. If you spend enough time with it, are willing to adjust your zero for elevation, and remember to readjust it when you reinstall the 5.56 bolt, this would make an excellent option compared to relying on a separate dedicated rimfire rifle.

Other Offerings

Perhaps you have a different take on ammunition types. Say you prefer 300 BLK to 5.56 NATO or 45 ACP to 9mm; CMMG offers upper receivers in a host of different calibers, including 5.7×28, 6.5 Grendel, 6mm ARC, 40 S&W, 350 Legend, and many others. The 22 conversion bolt only works with 5.56 uppers though. If you have a stockpile of Glock, Colt, or SIG 9mm magazines, there are uppers available for those as well. Some calibers may require an adjustment to the buffer system, but we didn’t run into any issues with the 9mm and 5.56 upper receivers we tested.

CMMG Resolute Magazines
Because the outward dimensions of the 22LR and 9mm magazines are the same as a 5.56 magazine, you can fit them into the same pouches without having to invest in another setup for new calibers.

Without question, the AR-15 has become America’s rifle, and manufacturers’ numbers bear this out. When taken as a whole and compared to other rifles that have been in production far longer, it’s evident how incredibly popular the rifle is in the United States. If you want to try an AR in a new caliber you don’t currently own, all you need is a different upper receiver. 

CMMG Upper Group Kit, Resolute 300, Mk4, 5.56x45mm 

CALIBER: 5.56x45mm
BARREL: 16.1 inches, 1:7 twist, medium taper, 4140CM, SBN
MUZZLE: CMMG SV Brake, threaded 1/2-28
RECEIVER: Forged 7075-T6 AL M4 type upper. Complete with BCG
FINISH: Hard-coat anodized (can be upgraded to Cerakote)
CHARGING HANDLE: CMMG oversized ambidextrous
WEIGHT: 6 pounds, 7 ounces
LENGTH: 25.3 inches
MSRP: $775

CMMG Upper Group Kit, Resolute 300, MkGs, 9MM

CALIBER: 9x19mm
BARREL: 16.1 inches, 1:10 twist, medium taper 4140CM, SBN
MUZZLE: SV Brake, threaded 1/2-28
RECEIVER: Forged 7075-T6 AL M4 type upper
FINISH: Hard-coat anodized (can be upgraded to Cerakote)
CHARGING HANDLE: CMMG oversized ambidextrous
MAGAZINE: 30-round 9mm AR conversion magazine (3 included)
MSRP: $1,030

SOUSA  Mantis 1-6x24mm

SOUSA Mantis 1-6x24mm

Magnification: 1-6x
Objective: 4mm
Tube Diameter: 30mm
Length: 11.5 inches 
Weight: 18.3 ounces
Exit Pupil: 4 to 11mm Exit Pupil
Reticle: Etched illuminated BDC second focal plane reticle
Field of view: 19 to 116 feet
Eye Relief: 5 inches
Adjustments: ½ MOA
Parallax: 100 yards
MSRP: $250

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