CMMG Guard versus Thompson Autorifle

[zaitcev]

CMMG just announced their Guard series of delayed blowback .45 ACP ARs. However, publications that I found fail to explain how their Radial Delayed Blowback system works. Fortunatley, VSO Gun Channel video at Full30 contains a couple of pictures that do explain. Video is here:
https://www.full30.com/video/27905dca4fc11e564fd1dd81f3364ea2

In the old Autorifle, the mechanical disadvantage was single: the pitch of the interrupted threads governed the amount of the disadvantage. The trouble was that required disadvantage was too great, so threads needed to be very fine (relatively), and that made the rifle sensitive to ammunition. To make it work, Thompson made the angle borderline suitable, with disadvantage reduced, which caused famously violent ejections. Red more about it here:
https://www.forgottenweapons.com/ria-thompson-model-1923-autorifle/

In Guard, disadvantage is compound: the cuts on the bolt create the rotation, which acts against the opposite angle on the carrier cam cut. Thus, the carrier and bolt act together much like they do in HK roller-delayed or Kirali lever-delayed blowback actions. The main disadvantage is between the carrier and the bolt, and the angle of the surfaces into which the locking is performed is only there to impair the motion into the carrier.

After I examined the VSO video, I became cautiously optimistic about the CMMG system. Its operation should not degrade due to the normal wear over the lifetime of the weapon. I just wish CMMG added a page with explanations to their website, so that prospective buyers were assured that we aren't seeing an Autorifle redux.

 

[zaitcev]

I should've named the thread "CMMG Guard versus Everything", but apparently the main point of the gun is that it's a true AR, mostly, and it delivers the best of modern modular platforms. For example, they chose to use Glock magazines and made the bolt stop work, which is not possible in the lowers using Grease Gun or Uzi magazines.

Flint River Armory's CSA45 is impressive in its performance, and it's amazing how competitive they are with Guard on price, considering their piston operating system. Cheapest CSA45 comes in at $1495 for a pistol, cheapest Guard at $1299.95. Unfortunately, they give up a lot of AR in the process. Their gun is AR-like, not AR.

I think the stiffest competition for Guard comes from Bazooka Brothers with RMW Extreme upper, at least performance-wise. I don't know how well they are set up to fulfill orders. But it's a DI upper and it is an AR. The only downside is that they chose to use Grease Gun magazines. They asking price is $1235 for a carbine.

The rest of the guns are blowbacks and we know that they require heavy bolts. And with Olympic Arms gone, nobody attempts to stuff that reciprocating mass into AR upper anymore. Thus, TNW Aero Survival Rifle uses a proprietary upper. MPA1SST is a re-imagined Ingram and is even further away from AR. And well, Vector Uzi is an Uzi.

So yeah, I very much welcome CMMG.

P.S. Macon Armory makes nice-looking DI uppers and conversion kits. But they do not offer a complete gun, AFAIK.

P.P.S. You can always have a Thompson by Auto-Ordnance, if your bicepsii are strong enough to lift it.

 

[browningguy]

For that price you could have an HK USC, I can't imagine a more accurate PCC than that.