Anyone tried the new CMMG Guard

[TGibe]

Ordered my upper this morning. Was hoping for some discount code or something, but didn't find anything... Fingers crossed that this thing runs well.

[bmiller]

I tried to put my guard upper on a colt lower. With the ejector out, the bolt will not clear the feed ramp. 

[TGibe]

7 minutes ago, bmiller said:

I tried to put my guard upper on a colt lower. With the ejector out, the bolt will not clear the feed ramp. 

 

While I'm sure I could get my NFA lower to work with the mod, I ordered a lower from CMMG yesterday. This way I can leave my current PCC as is for a spare... maybe eventually sell it as a complete unit.

[bmiller]

At a closer look, there are more differences with the guard bolt than I noticed originally. The .556 bolt is on the left. 9mm guard on right.  I am pretty sure a conventional barrel extension will not work due to the differences in bolt lug pattern.  The bolt face of my .556 bolt is .380" across inside. The guard bolt is .395.  

[bmiller]

Here I see the pic of a Colt pattern lower on the guard upper. I think it will take significant massaging of the feed ramp to get this to work.

[Marshal82]

23 minutes ago, bmiller said:

At a closer look, there are more differences with the guard bolt than I noticed originally. The .556 bolt is on the left. 9mm guard on right.  I am pretty sure a conventional barrel extension will not work due to the differences in bolt lug pattern.  The bolt face of my .556 bolt is .380" across inside. The guard bolt is .395.  

 

Lug pattern is the same, The normal Barrel Extension should work (well might has to adjust for feeding). The Guard bolt just has the bottom lugs ground on the side to pass a 9mm glock mag feed lips.

 

The Bolt Face is different because the rim of a 9mm case is larger than a .223/5.56

[bmiller]

I put them face to face.  I was wrong.  There is just material removed from the side of  lower lugs.

[BartCarter]

So, what uppers will these work with?  I am looking at normal 5.56 mil-spec, 9 mm cut slick sided and both that are available in side charger versions.

 

Would a 5.56 work with maybe a little clearance work in the ejection port area for 9 mm clearance?  This would mean that I would have functional dust cover and forward assist if I want.  Does the system need M4 feed ramps?

 

On the side charger versions, are there differences in the way the side charger cycles the BCG?  The GIBBZ uses a different cam pin for the  BCGs that need one.  I know the CMMG has a different type of cam pin than a 5.56, so am I good to go or would the GIBBZ supplied one work?   Is there a different side charger version that does not require a cam pin change?

 

CMMG has not done the trials and fittings of anything but their design, so they were unable to give me any advice on this.

[bwikel]

The Gibbz and NFA  multi-caliber side chargers will work without the special cam pin on a blowback 9mm bolt, I don't know if that translates to the CMMG bolt or not. 

[bmiller]

I am using it in a standard m4 flat top upper. My forward assist works fine. I didn't have to open up the ejection port. I don't own a side charging upper, so I don't know on that one. 

[BartCarter]

Thanks, Brian, I'll start with a standard upper.  I can decide later if I want to do something else.

[noexcuses]

Hmmm, how about the delayed blowback setup with a  5-8" barrel with with a  true comp and running slow powders (AC,HS6 ect) around 150PF. I wonder if the comp would work enough or would you have to run it up to major power to get the benefits of the comp like a open gun. Although you would not get major scoring. I like the idea of the delayed blowback for this as it would lessen the worry about a out of battery event.

[noexcuses]

X2

Edited December 3, 2017 by noexcuses
multi post

[noexcuses]

X3

Edited December 3, 2017 by noexcuses

[noexcuses]

X4  dont know how this happened, sorry 

Edited December 3, 2017 by noexcuses

[L9X25]

4 hours ago, noexcuses said:

Hmmm, how about the delayed blowback setup with a  5-8" barrel with with a  true comp and running slow powders (AC,HS6 ect) around 150PF. I wonder if the comp would work enough or would you have to run it up to major power to get the benefits of the comp like a open gun. Although you would not get major scoring. I like the idea of the delayed blowback for this as it would lessen the worry about a out of battery event.

 

You could say that again!   ;-)

[lgh]

3 hours ago, L9X25 said:

You could say that again!   ;-)

I'll quadruple that!

[noexcuses]

8 hours ago, L9X25 said:

 

You could say that again!   ;-)

and again and again and once more lol

[L9X25]

I know what happened to you, it happened to me when I initially replied.  The servers were bogged and it appeared that they did not accept the post, but they actually did.  I did not think that my smart-ass comment was worth typing again, and was just leaving the thread, then my message popped up.  I could have easily re-sent it multiple times before it appeared.

 

 

 

Edited December 4, 2017 by L9X25

[Honeybooboo]

So these seem like they are good to go huh? How do they compare to an MPX as far as shootability and recoil?

[bmiller]

I don’t have a tremendous amount of rounds on mine, but so far, so good.  I would say recoil is on par with an mpx. Definitely less than a blow back.  My blow back gun is very flat, the added recoil doesn’t seem to affect my times.  I think it pcc is just like any other division, get a good reliable gun and practice.

[TGibe]

Is the LRBHO tab the only thing keeping the mag from over insertion on the CMMG lower? Or am I not seeing it...?

 

My CMMG lower is backordered and when I tried the CMMG upper on my NFA lower I noticed that I had been running the NFA lower without any over-insertion protection all along.

 

Thanks,

Allen

 

On 11/25/2017 at 1:20 PM, BartCarter said:

Here you go.

 

 

 

[BartCarter]

On 11/20/2017 at 6:30 PM, BartCarter said:

...As you know, the lower on the Guard does not have an ejector.  It is on the bolt like an AR 15.  What they did to stop over insertion was to mill a ledge in the magwell that prevents over insertion by using the corresponding ledge on the Glock magazine.  I just tested a Glock mag on the lower (disengaging the mag release while testing) and that is the only thing stopping the mag from over insertion.  The LRHBO does not enter into this as a possible stop.

 

This ledge / mag fit doesn't allow for over insertion...

From page 1 

[BartCarter]

On 11/22/2017 at 1:10 PM, BartCarter said:

Here are pics of the mag stop ledge.

And then pics of the ledge stopping the mags from over insertion.

[bmiller]

1 hour ago, TGibe said:

Is the LRBHO tab the only thing keeping the mag from over insertion on the CMMG lower? Or am I not seeing it...?

 

My CMMG lower is backordered and when I tried the CMMG upper on my NFA lower I noticed that I had been running the NFA lower without any over-insertion protection all along.

 

Thanks,

Allen

 

 

On the NFA lower, over insertion is stopped by the ejector, it acts as a stop for the mag.  You have to remove the ejector from the lower to run the guard bolt because it is not slotted.  I have been machining stops that drop in place of the ejector of the NFA lower.  My NFA lower works great the the guard upper with the stop installed.