Don't know if you guys knew this but several people (myself included) have gotten the Guards to work with Colt mags....just CMMG doesn't support this configuration.
I am grateful that CMMG does sell the BCG and barrel seperately for those people that want to do their own builds.
This is discussed here:
https://www.ar15.com/forums/AR-15/Thoughts-on-the-CMMG-Guard-/15-713060/?page=6
I also go through all the details I did here:
http://c3junkie.com/?page_id=597
There really isn't much to it. Here is a video of it running in full auto, pulling singles and short bursts:
https://www.youtube.com/watch?v=cmAdCXDTUgc
All that said, I've never like the Colt mags. I do have a pile of them but I've had them fail on me too many times in subgun competitions running full auto.
I also hate how they 'volcano' if you drop them.
I also have the factory Guard Glock lower as my 'control' to do all my testing. What I've also found is that the Glock mags require less force to strip off rounds than the Colt mags.
Most people never notice this because 9mm Colt mags are typically used in blowback setups where you have a strong spring and a heavy bolt w/ a weight in it slamming forward....which also makes the gun bouncy....I absolutely detest the 9mm Colt blowback in full auto. I feel like kicking it down the street after shooting a full auto MP5 side by side.
Thank God CMMG came out with the RDB system as I now have a setup that I feel surpasses the MP5.
The Guard doesn't ship with any weight in the carrier but they do have the carrier drilled out to accept their tuning weights.
Less mass flopping around is going to give you a smoother experience but is also less force to strip rounds off.
Regarding magazines, less force required to strip rounds off = a larger operating window of reliability....but I really didn't want to use the single feed Glock mags either.
Now that the Mean Arms Endomags came out, I'm really happy with those. Double feed and I'd say on par with the Glock in regards to force required to strip rounds. For training purposes, same pouches I use for 556 as well.
You don't have mod anything in a standard AR lower to use the Endomags....you just need to order the Endomags cut for the CMMG Guard since the Guard relies on the ejector in the bolt.
This is a video of that running in full auto with two different 8" Guard BCG/Barrel assemblies:
https://www.youtube.com/watch?v=_XaGtM2NT38
In the first part of the video I'm running the first 8" Guard BCG/barrel assembly I purchased, this earlier barrel came w/ 1/2-36 threads and the barrel extension had the dual M4 cuts which is odd since CMMG only sells single feed Glock lower setups.....I think they just didn't have time to get custom extensions made that had a single feed ramp at the time.
The latter part of the video, I'm running the second 8" Guard BCG/barrel assembly I purchased, this barrel came w/ 1/2-28 threads and the barrel extension had the single feed ramp cut for obviously the single feed Glock mags.....however, I made no mods to the extension and as you can see in my video, it is working fine with the dual feed Endomags.