CMMG Guard tuning (9mm)

[cking]

CMMG responded the weights are standard in blow back gun not in the guard, got no response on the change in felt recoil, I'm still going buy a set and see what effect they have.

[ziebart]

Anyone have issues with Glock OEM mags falling out of the CMMG lower prior to hitting the magazine release? All of my mags will except the Magpul brand. CMMG said it was because Glock changed the specs on the mags and to use ETS mags but I've got mags going back a decade and they all do the same. ETS will fall free too. 

 

[HDSledge]

11 hours ago, cking said:

CMMG responded the weights are standard in blow back gun not in the guard, got no response on the change in felt recoil, I'm still going buy a set and see what effect they have.

I have not been able to get to the range to test my Banshee upper with my AR-15 lower.  Interested to see how things go for you with the tuning kit.  

 

Remind me please do you have a Guard upper on a AR15 lower?  If so which buffer/spring are you using?

 

A member at arfcom has tested extensively and relates that his best running setup is with an A5 tube, Tubb flat 5.56 spring, and a Blitskrieg 9mm hydraulic buffer.  He says it works well with his 5.56 upper as well.  He tuned for rate of full auto fire as well as felt recoil.

[BartCarter]

2 hours ago, ziebart said:

Anyone have issues with Glock OEM mags falling out of the CMMG lower prior to hitting the magazine release? All of my mags will except the Magpul brand. CMMG said it was because Glock changed the specs on the mags and to use ETS mags but I've got mags going back a decade and they all do the same. ETS will fall free too. 

 

 

All my 33 round Glock mags work perfectly.  I have never heard of this before.  My 1st Guard shipped with a 33 round Glock mag.

[ziebart]

10 hours ago, BartCarter said:

All my 33 round Glock mags work perfectly.  I have never heard of this before.  My 1st Guard shipped with a 33 round Glock mag.

Mine shipped with a Glock mag too. I think the catch is slightly too small in mine or something. As the magazine wiggles it will drop out. It was hard to diagnose at first because it was having a lot of fail to feed as the magazine was slightly out of position preventing the bolt from grabbing the round correctly.

[BartCarter]

51 minutes ago, ziebart said:

Mine shipped with a Glock mag too. I think the catch is slightly too small in mine or something. As the magazine wiggles it will drop out. It was hard to diagnose at first because it was having a lot of fail to feed as the magazine was slightly out of position preventing the bolt from grabbing the round correctly.

CMMG has been very good with customer service.  I'm sure they would fix the problem.

 

My CMMG Guard lower is made especially for the Glock mags.  There is a ridge to prevent overinsertion and position the mag correctly.  Have you taken the lower by itself and checked to see how the mags are seating and locked in? 

[ziebart]

Yes they answered their emails but i don't really have the problem fixed. They said it was due to me inserting a full magazine with the bolt closed. While I may have done that on some of my mags, it wasn't done to all of them.

 

The mags do the same thing with the upper off the gun, and will wiggle free.

[BartCarter]

2 hours ago, ziebart said:

...The mags do the same thing with the upper off the gun, and will wiggle free.

 

That calls for a return for repair as I see it.

[NPDriver]

What is the best way to limit the height to prevent over-insertion insertion of the magazine? I have the Guard guts installed in a FM products build kit that does have a stop milled into the magwell. I'm usually inserting the magazine on an open bolt so it's not a huge issue, but I am noticing my brass is getting a bit scraped up. I'd prefer not to make any permanent changes to the lower, I'll just pick up an extra mag release and mill a bit off the top of the one I have. I'm thinking some sort of stop extension that just bolts in where the ejector once sat. It's running well as is, I'd just like to know that I'm good to shoot prone or off a bench monopoding off the magazine. 

[MemphisMechanic]

@NPDriver I modified the ejector in my KE Arms lower to clear the bolt and turned it into a mag stop. The gun is at roughly 800 rounds without any malfunction of any kind since this modification. You can shoot the gun monopodded on a magazine and it runs perfectly.

 

It did require welding up the opening in the ejector and then some work with a grinder and belt sander. [EDIT] oh yes, and bending the ejector outwards to clear the bolt carrier - it needs to run in that groove in the carrier’s underside so it won’t rub.

 

I also had to lower the magazine height by approximately 1/8” or more in order to get the larger Guard bolt face to clear the feed lips in a lower designed for a blowback bolt. Shaved material off the magazine release.

Edited January 21, 2019 by MemphisMechanic

[HDSledge]

Got my Banshee upper tuned very well with my Spike's lower and a Magpul CTR stock using a Kynshot RB 5005 hydraulic buffer and a standard carbine round wire spring.   Blazer Brass FMJ using an Endomag insert in a Pmag gen 3.   3k rounds downrange so far without FTF/ FTE.  ~666 RoF.

CMMG Banshee upper on Spike's Cal-Multi Lower, Endomag Pmag insert, KAW Fat LC

Edited January 21, 2019 by HDSledge

[NPDriver]

Thank you! I've been thinking much along the same line. Using the ejector as the starting point for a spacer. The fact that it's removable would just make it so much easier to work and make adjustments. I thought about using an epoxy to add material to the stop or tacking a spacer under it, then again I'm hesitant to make any permanent changes that I may regret later. I want to keep my options open so I can swap to any upper by just changing mag releases, ejectors and buffer systems. 

Edited January 21, 2019 by NPDriver

[HDSledge]

Posting my experience with a non 9 CMMG lower is off topic.  Sorry.  Not sure why I didn't realize that, maybe because I have never owned one.  Still enjoy reading the great info in here.

Edited January 21, 2019 by HDSledge

[NPDriver]

 

4 minutes ago, HDSledge said:

Posting my experience with a non 9 CMMG lower is off topic.  Sorry.  Not sure why I didn't realize that, maybe because I have never owned one.  Still enjoy reading the great info in here.

No it's cool man! I'm glad to hear you're having the success with your rig that you are. This was my first build and I was wondering if I was making a mistake by taking a different path than others. I'm happy to know that I'm not on my own and I have a few guys out there to bounce ideas off of. I haven't got my buffer system nailed down yet. Just running a standard carbine weight & spring for the time being so I'm open to all suggestions. Sounds like the Endomags are working fine by the video clip?

[MemphisMechanic]

1 hour ago, NPDriver said:

I thought about using an epoxy to add material to the stop or tacking a spacer under it...

 

Epoxy isn’t strong enough - not for how much of the original material I removed. I had to cut ALL of the original steel off the top of the window on my ejector. Put a spacer under it? On the contrary: I had to cut 1/4” or so off of it in order to make it sit lower in the slot.

 

I think some companies might use a solid ejector without a window in it. If so, buy one and start with that! You won’t need to weld... just file, cut, and sand.

 

<<EDIT! Jackpot! Buy a couple of these so you have a spare, and take a dremel cutoff wheel or a hacksaw to the top and bottom as seen below. No epoxy or welding needed.>>

 

https://www.newfrontierarmory.com/shop/ejector-c9-c45/

 

Quote

then again I'm hesitant to make any permanent changes that I may regret later.

 

Carve an ejector up. They’re cheap and easy to buy and easy to replace. It’s not forged into the lower, man!  

 

Edited January 21, 2019 by MemphisMechanic

[MemphisMechanic]

For those who aren’t aware, a CMMG Guard bolt looks exactly like a 5.56’s. Gear teeth. Pin style ejector in the bolt face. Etc.

 

So you have to remove the ejector from a blowback lower in order to run a Guard bolt & barrel on it. But the ejector is also your magazine stop, which keeps mags from overinserting if you load the gun with the bolt open.

 

Here’s how I modified the ejector to ride the magazine on top of the metal feed lip and firmly set magazine height between the mag catch and this new stop.

 

I do not recommend this with aftermarket  mags. ETS and other mags have plastic feed lips which are thicker: If you set this up for  Glock mags you get steel on steel. Insert an ETS  mag and it won’t lock into the gun. You need to readjust ejector height, and metal riding on that brittle ETS plastic made me nervous about wear.

 

Factory setup: nowhere near clearing the large Guard bolt, even if you do lower the ejector til it contacts the mag:

 

 

Filled in the top of the window of my KE Arms ejector with a quick MIG weld:

 

 

Ground the top down as thin as I dared, then removed steel from the bottom so it can ride lower in the ejector slot of the reciever:

 

 

Complete. Side view:

 

 

Bent sideways until it clears the gear teeth of the bolt, rides in the slot in the carrier, and also rests directly atop the steel liner of the magazine feed lips:

 

(for this step, paint the stop with a sharpie and cycle the gun. Continue adding more bend until the sharpie isn’t scrubbed off when you cycle the bolt.)

 

 

Runs flawlessly:

Edited January 21, 2019 by MemphisMechanic

[NPDriver]

I think you misunderstood what I was saying. The ejector on a FM lower is only the ejector. There is a stop milled into the magwell to limit the height of the magazine. I was talking about adding material to that. It should only take a small amount of added material as I already have something to build from. That was one of features that sold me on their lowers, I knew I'd have somewhere to start.

[MemphisMechanic]

Ahh! Never seen an FM lower - nothing is standardized in AR9’s and there are so many damn brands!  

 

Okay, that might indeed work. Although using my approach might be easier than trying to file/dremel down material inside of the magwell opening.

 

Nonetheless, I hope my post helps the next guy looking to build a Guard on a conventional 9mm lower even though it may not apply to yours. 

 

Good luck and keep us posted on what you figure out.

 

[HDSledge]

58 minutes ago, NPDriver said:

 

No it's cool man! I'm glad to hear you're having the success with your rig that you are. This was my first build and I was wondering if I was making a mistake by taking a different path than others. I'm happy to know that I'm not on my own and I have a few guys out there to bounce ideas off of. I haven't got my buffer system nailed down yet. Just running a standard carbine weight & spring for the time being so I'm open to all suggestions. Sounds like the Endomags are working fine by the video clip?

 

Yes the endomags are reliable.   A lot of us who pre-ordered were skeptical at first and then pleasantly surprised.   I wasn't going to trust them until I fired a bunch of rounds with no problems.  I feel very comfortable keeping the Banshee upper on my lower in case the shtf.

Edited January 21, 2019 by HDSledge

[HDSledge]

Has anyone noticed a weakening of the ejector spring?  It is happening consistently to a member on another forum who shoots suppressed full auto.  Mine is still pretty stiff but I don't have my suppressor yet.

[bwikel]

I had a couple stoppages due to poor extraction so I swapped my extractor and ejector springs over to extra power versions and change them annually now.  

[MemphisMechanic]

29 minutes ago, bwikel said:

I had a couple stoppages due to poor extraction so I swapped my extractor and ejector springs over to extra power versions and change them annually now.  

 

It runs standard 5.56 springs in those locations, correct? I’ll pick up some and install preventatively. Keep an extra pair as spares.

[BartCarter]

1 hour ago, bwikel said:

I had a couple stoppages due to poor extraction so I swapped my extractor and ejector springs over to extra power versions and change them annually now.  

How many rounds until you see a change?

[bwikel]

2 hours ago, MemphisMechanic said:

 

It runs standard 5.56 springs in those locations, correct? I’ll pick up some and install preventatively. Keep an extra pair as spares.

Yes standard AR bolt and carrier springs. There are several companies that make an extra power version. 

[bwikel]

1 hour ago, BartCarter said:

How many rounds until you see a change?

My issue happened around 5k.