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CMMG Guard tuning (9mm)


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13 minutes ago, bwikel said:

Full auto no but I do run some suppressed. 

 

I'm at around 3k rounds unsuppressed.   I will be ordering a couple spare springs and will visually compare with my original one. 

 

There is discussion about the ejector spring overcompressing and wearing out too fast (hundreds of rounds, not thousands) in the Guard suppressed with some buffer/spring combinations.  Rapid spring fatigue reported with low RoF suppressed full auto setups.  Would a rounded edge 1/16" titanium rod inserted into the spring limit travel of the ejector without chewing up the inside of the spring?  Or an ejector machined with a post into the spring to limit travel?

 

Still learning so if that idea is bonkers I won't get my feelings hurt.  :)

Edited by HDSledge
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On 1/21/2019 at 4:10 PM, MemphisMechanic said:

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

 

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. 👍

 

No, I like seeing what other people are up to. I lurked around this forum for months before creating an account. I learned a lot by going through old threads and reading about problems and solutions that people come up with. It's good to put this stuff out there. You never know who's reading this & trying to educate themselves. 

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30 minutes ago, MemphisMechanic said:

 

Will do! Finally got the magazine release out to shave a bit off after stripping the allen screw. Had to pound a torx bit into it to break it loose. They had some hellacious thread locker on that thing from the factory.

Mental note- throw some heat on anything else I need to remove. 

 

BTW, how do I shrink photos to .49MB?

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Anyone had trouble with theirs not chambering a round because the bolt hangs up on the round still in the magazine? 

 

I'm using Berry 124 round nose loaded at 1.153 COAL, 3.2 gr titegroup, about 135 PF. Doesn't happen often, probably 1 in 50 rounds. Rounds seem to drop free from chamber so I don't think they are too long. 

 

Gun has already been back to CMMG once due to feeding issues and they said it was due to me inserting fully loaded mags on a closed bolt. In that case the mags were damaged and would fall free without touching the magazine release.

20190203_172155.jpg

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I haven't experienced anything like that but I have to insert my mags on an open bolt. I'm using a lower that's currently holding the mag a bit too high in the magwell to load it any other way. My casings are getting scratched up a bit from the lugs on the bolt dragging while cycling, but nothing like that. 

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On 2/2/2019 at 11:44 AM, bwikel said:

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

 

Which brand of extra power springs did you use? I couldn’t find extra power ejector springs, and a Wolff extra power AR15 extractor spring does not fit under my Guard extractor. 

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15 hours ago, StealthyBlagga said:

 

Which brand of extra power springs did you use? I couldn’t find extra power ejector springs, and a Wolff extra power AR15 extractor spring does not fit under my Guard extractor. 

These are the ones I used. I'm not sure if the ejector spring is considered "extra power" but it was longer than the stock spring and tough to compress in the bolt. The extractor spring is an extra power version and it will fit under the extractor without an o-ring but the tension is significantly more than the stock spring. 

 

http://www.davidtubb.com/ar15-extractor-ejector

Edited by bwikel
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23 hours ago, bwikel said:

These are the ones I used. I'm not sure if the ejector spring is considered "extra power" but it was longer than the stock spring and tough to compress in the bolt. The extractor spring is an extra power version and it will fit under the extractor without an o-ring but the tension is significantly more than the stock spring. 

 

http://www.davidtubb.com/ar15-extractor-ejector

 

Awesome, thanks - just ordered from Brownells :)

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7 hours ago, HDSledge said:

 

Hey did you guys start out with the .45 springs that CMMG installed?  They are sending me a new ejector spring to compare with mine for wear.

I started with the stock springs that came in my guard bolt. I don't have a complete factory guard, I built off a bolt/barrel package. 

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3 hours ago, bwikel said:

I started with the stock springs that came in my guard bolt. I don't have a complete factory guard, I built off a bolt/barrel package. 

That was probably the old spring they used to start.  Since then they replaced them with stiffer .45 springs.

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1 hour ago, HDSledge said:

That was probably the old spring they used to start.  Since then they replaced them with stiffer .45 springs.

I would agree since my guard parts were some of the first produced, I got them in Dec. of 2017.

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  • 1 month later...

Sorry to revive an old thread but I've recently been trying to get my guard tuned for uspsa pcc.  It's a home built guard using the 16inch barrel bolt combo, cmmg clearanced upper, and guard lower with a cmc pcc trigger. 

 

 Im currently running the 2oz carrier weight along with a Tubbs flat wire spring.  I've shot a total of probably 3000 rounds through the guard total. The first 1500 were all factory Blazer brass but once I got the extended mags from taylor freelance (goliath) and the mega from mbx, the rounds wouldnt feed reliably at all.  Turned out those rounds were too long oal.  Switched to Remington umc and it's been fine for the last 1500 rounds.

 

Ive got a bit more time now so I started trying to get some good handloads for it, so I tried some 124g berrys bullets with 3.1g titegroup. I ran a match last weekend and had a double feed on nearly every stage with the handloads.  In doing research on the best handloads people are using for PCC I went down the rabbit hole reading about the different buffer systems people are using for pccs. 

Is there any consensus on the best buffer and spring combos to use with the guard? Since the guard uses a standard length buffer which ones are not compatible (without going to an a5 tube)? List which buffer system you like and what your load is please

Edited by ferch
Typo fixes
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On 10/15/2018 at 8:19 PM, MemphisMechanic said:

 

Here’s mine. I just opened up the front half of the port as wide as makes any kind of sense. Then a pinch more

 

458 socom port? Nah. Keep going.

 

(Click the photo and swipe for a better view)

 

 

What castle nut and end plate are these? Thanks.

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Ferch,

 

I had a lot of issues with the mags falling out and feeding. Eventually CMMG sent me a new mag catch. It might help your issues, but I didn't have any double feeds.

 

I am using 124 Berry's RN at 1.10 COAL and 3.2 gr titegroup. Seems to be working with stock components but we will see. 

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On 3/27/2019 at 3:24 AM, ziebart said:

Ferch,

 

I had a lot of issues with the mags falling out and feeding. Eventually CMMG sent me a new mag catch. It might help your issues, but I didn't have any double feeds.

 

I am using 124 Berry's RN at 1.10 COAL and 3.2 gr titegroup. Seems to be working with stock components but we will see. 

Ziebart-

Which weight do you have in the bolt carrier, and what kind of buffer/spring setup are you running?

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On 3/26/2019 at 5:43 PM, ferch said:

I tried some 124g berrys bullets with 3.1g titegroup. I ran a match last weekend and had a double feed on nearly every stage with the handloads.

 

I’m sure you did. A PCC is not a handgun, so don’t treat it like one. Load 140-145pf or so and it’ll shoot just as fast and flat as with the 130ish PF ammo, unlike a handgun where lower velocity poses a small advantage.

 

Try it again with 3.5 to 3.8 TG.

 

Edited by MemphisMechanic
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On 3/26/2019 at 7:30 PM, jualdeaux said:

What castle nut and end plate are these? Thanks.

 

On 3/26/2019 at 8:59 PM, NPDriver said:

Looks to be a Strike Industries endplate & castle nut. Hey MemphisMechanic, didn't you end up swapping out the Colt lower for a KE Glock lower?

 

NPD is correct, they’re Strike’s. Pure bling factor, no advantage otherwise.

 

Yes. F%*# some Colt mags, the Guards should run on Glock mags if you want an easily reliable setup.

 

I had to modify the Colt mags to sit lower in the QC10 lower, and had to modify the KE lower to get the Glock mags to sit low enough in that. The Guard needs a mag 1/8” to 1/4” lower than a blowback gun does.

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