CMMG announced its MkG GUARD has been tested, and safely rated for 450 SMC. The AR15 rifle is chambered in .45 ACP, feeds from factory Glock magazines and features the Radial Delayed Blowback operating system, which works to harness the strong recoil impulse of .45 ACP.
Triton first conceived the 450 SMC design in 2001. Years later, DoubleTap ammunition took over the design and completed it. Essentially, it is a magnum version of .45 ACP, offering ballistics comparable to 10mm.
While the 450 SMC's casing is identical to that of .45 ACP, there are modifications allowing DoubleTap to load 450 SMC with five to six thousand pounds per square inch of pressure more than a standard .45 ACP. First, the 450 SMC uses a small magnum rifle primer rather than large pistol primer, allowing the hardened case to be thicker at the base. Second, the brass is manufactured to handle up to 30,000 pounds of pressure, resulting in a cartridge capable of taking down big game.
Although 450 SMC can be safely run in any .45 ACP rated for +P ammunition, the amount of rearward force might potentially be problematic from a straight blowback AR15. The Radial Delayed Blowback operating system prevents this issue for CMMG's GUARD.
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, mitigating the leftover rearward force and driving the carrier back to cycle the action. By eliminating some rearward force during the unlocking sequence, the GUARD requires less weight in the bolt carrier group and buffer to safely cycle. Thus, resulting in the end user experiencing less recoil.
Here's how the 450 SMC stacks up against 10mm out of a 16-inch barrel (data provided by DoubleTap Ammunition):