You might recall that I purchased a CMMG .45 ACP PSB, CMMG’s AR pistol in .45 ACP.  I did a brief review of it and found it to be very much to my liking, eating everything I could put in it with no FTF/FTE over 300 rounds.  It may be the best gun purchase I’ve ever made.  Well, this development increases their capital.

CMMG’s MkG Guard pistol-caliber rifle is now safety certified to shoot the potent 450 SMC cartridge, according to a recent CMMG press release.

The CMMG MkG Guard is an AR15-style rifle for chambered in .45 ACP and features a Radial Delayed Blowback operating system that works to harness the strong recoil impulse of .45 ACP.

Pistol-caliber carbines and rifles are becoming increasingly popular in the shooting community.

For those unfamiliar with 450 SMC, Triton first conceived the cartridge in 2001 and is essentially a magnum version of .45 ACP that offers ballistics comparable to 10mm.

“It is a true stopper that delivers energy capable of taking down big game,” the release states.

For example, the 450 SMC 185 grain Bonded Defense jacketed hollow point round will produce a muzzle velocity of 1,725 feet per second and 1,223 foot pounds of energy out of a 16 inch barrel, the release states.

While the 450 SMC uses a case with the same outer dimensions as .45 ACP, there are a few significant differences that allow DoubleTap Ammunition to load 450 SMC with five to six thousand pounds per square inch of pressure more than a standard .45ACP, according to the release.

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, the release states. But the CMMG’s Radial Delayed Blowback operating system allows the Guard to handle the potent load, CMMG officials maintain.

The RDB 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, which will result in less felt recoil for the shooter, CMMG officials maintain.

I won’t get 1725 FPS out of my shorter barrel, but by using the 450 SMC cartridge I should see an improvement of 200-300 FPS over the .45 ACP based on what I’ve read.  I also wrote tech support at CMMG to verify that their position holds not just for their carbine, but for the AR pistol as well.  It does.