CMMG MkG Guard Takes On the .45 ACP Magnum?

450 SMC from DoubleTap ammunition

CMMG’s MkG Guard is an AR-15 rifle that is chambered in .45 ACP and feeds from factory Glock magazines. At the heart of the Guard is the patent pending Radial Delayed Blowback operating system that works to harness the strong recoil impulse of .45 ACP. After extensive durability testing, CMMG is proud to announce that the Guard is safely rated for 450 SMC.

CMMG MkG Guard in 450 SMC with combat light and red dot optic
CMMG MkG Guard

For those unfamiliar with 450 SMC, Triton first conceived the cartridge in 2001. The design was ultimately taken over and completed by DoubleTap ammunition years later. In essence, it is a magnum version of .45 ACP that offers ballistics that are comparable to 10mm. It is a true “stopper” that delivers energy capable of taking down big game.

While the 450 SMC uses a case with the same outer dimensions as .45 ACP, there are a few significant differences that allow DoubleTap to load 450 SMC with five to six thousand pounds per square inch of pressure more than a standard .45ACP. First, the 450 SMC uses a small magnum rifle primer instead of the large pistol primer. This modification allows the hardened case to be thicker at the base.  Second, the brass is manufactured from the ground up to handle up to 30,000 pounds of pressure. The result is a dual-purpose cartridge that is exceptional for both hunting and personal defense.

While 450 SMC can be safely run in any .45 ACP that is rated for +P ammunition, the amount of rearward force created by such a hot load would potentially be problematic from a straight blowback AR15. CMMG’s Guard platform can overcome these issues, however, thanks to the Radial Delayed Blowback operating system.

four boxes of double tap ammunition The Radial Delayed Blowback system uses up some of the recoil impulse of the spent round to unlock the rotating bolt from the barrel extension. This mitigates the leftover rearward force that then drives the carrier back to cycle the action. By eliminating some of this rearward force during the unlocking sequence, the Guard requires less weight in the bolt carrier group and buffer to safely cycle. This reduction in reciprocating mass results in less felt recoil for the end user.

Here’s how the 450 SMC stacks up against 10mm out of a 16-inch barrel (Data provided by DoubleTap Ammunition):

450 SMC
Doubletap Ammunition Muzzle Velocity Muzzle Energy
450 SMC 160 gr. Barnes TAC-XP Lead Free 1,740 fps 1,076 ft-lbs
450 SMC 185 gr. Bonded Defense JHP 1,725 fps 1,223 ft-lbs
450 SMC 230 gr. Bonded Defense JHP 1,400 fps 1,001 ft-lbs
450 SMC 255 gr. Hardcast Solid 1,300 fps 958 ft-lbs
Doubletap Ammunition Muzzle Velocity Muzzle Energy
10MM 165 gr. Bonded Defense JHP 1,700 fps 1,059 ft-lbs
10MM 180 gr. Bonded Defense JHP 1,600 fps 1,023 ft-lbs
10MM 200 gr. Hardcast Solid 1,590 fps 1,123 ft-lbs
10MM 230 gr. Hardcast Solid 1,350 fps 931 ft-lbs

Do you believe the 450 SMC will become a force in the market? What is your favorite AR-15 caliber? Share your answers in the comment section.

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Comments (14)

  1. Hmmm. I’ve still got 45 rounds of factory .45 magnum ammo and 500 new primed .45 magnum cases.Shot this in a Contender barrel. I’ll have to chrono this .45 magnum to see how it compares to the 450.

  2. Great idea that has been chased before. With all the new hoopla over the 10MM, it is a perfect time to finally make it happen. The loads listed are a perfect match with recoil management and enuough power to stop any threat, two legged, or four. If this round lasts with the popular media casting out plenty of sound new calibers. It’s likely the leaders in the market will want to snuff it out. You don’t need another 1911. Or a carbine in a pistol round. Thus less marketable products.
    I am hopeful it will last. I own many quality Arms. This round brings much more out of many. It also brings to life the .45ACP+P firearms, making them into a much more useful Deer hunting tools.

  3. Would expect S R & Co. to offer these in some other chamberings in the future, i.e. , .30 M-1, 10 mm , .460 S&W .Luv my Marlin Camp Carbine bought in `92, in .45 acp , uses 1911 mags.

  4. The 460Rowland requires a conversion…. barrel/compensator/…

    The 458 Socom doesn’t shoot out of my common 45acp caliber 1911, Glock, carbine, revolvers, pistols….

    Sad that Triton went bankrupt. Glad that DoubleTap bought bankruptcy assets and re-released the 450SMC. It makes my 45auto as powerful as it should be and I can use 45ACP, 45ACP+P, and 450SMC ammo all in my common single caliber revolver, handguns, carbines, rifles….

    Using 450SMC is as simple as swapping the box of ammo, even though I might recommend a stronger or newer not worn out recoil spring, new or upgraded magazine spring, and some common sense testing. Its not for worn out junk guns, but nor is 45ACP+P.

  5. The hot loaded 45 ACP niche has long been filled by several similar cartridges such as the 460 Rowland and 451 Detonics. This new round may be hotter, but to what end? I can’t think of a standard pistol platform I’d care to shoot it from, and when it comes to large diameter carbines, the 45 Winchester Magnum, 450 Bushmaster, and 458 SOCOM equal or exceed it. But I suspect it will develop a following.

  6. because the 460 Rowland already exists, and is about the same thing, only advertising hype would drive people to buy the “new” thing that already exists. just like the 6.5 Creedmoor, which came out years after the superior .260 Remington. I can see no reason for putting this in an AR platform, when the .458 SOCOM already exists, and works, there will be a few people that might be tempted, but there are already weapons out there that are better suited for pistol cartridge carbines than an AR that use Glock mags. but that’s just my 2 cents.

    1. The 357 Sig is my choice. I own an FNP in this as well as a Glock 31. Great cartridge. Never used on biological targets but the 9mm+P has worked great for me in the past. A 45 acp necked to 40 S&W would be even better but I’m sure it’s been attempted but I personally haven’t heard of or seen. Semper Fi.

    2. @ SSgt Herrington.

      I don’t it’s possible to “Neck-Down” a .45 ACP Cartridge without “Buldging” the remaining brass! At least I’ve NEVER heard of it being done…

    3. Close to the 45ACP necked down to a 40S&W is the 40 Super.
      40 Super is a 45 Win Mag case necked down to .40.

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