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CMMG FTE


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I have an original 16" 9mm Guard upper and a new 8" CMMG upper.  I'm shooting both on an ADM lower.  The long barrel runs everything including very soft (2.8 gr Sport Pistol/115gr coated) while the short barrel won't consistently eject 3.6gr loads with the same bullet.  The 8" won't run 147gr Winchester PDX.  It's got to be the bolt so I'll swap bolts at the next range session.  Strange that this would happen with a new upper as I thought CMMG has resolved the ejector issues.  Did talk to Brian at CMMG and he wants to know what I find.  Obviously, they'll send me replacement parts if needed.  The 8" version is a sweet gun to shoot. 

 

As always any/all suggestions appreciate.

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16 minutes ago, BartCarter said:

I'd like to know what you find too.  CMMG has worked with many people to resolve these types of issues.  Reading many posts, the issues seem to get resolved one way or another.

Of course.  I do have the advantage of two CMMG uppers.  I won't bother to chrono, but I wouldn't expect much more than a 100 fps difference between the two barrel lengths.  Regarding the PDX FTE that stuff makes for a good "thump" in our 9mm 1911s to it certain should cycle.  I've put a BCM lower on the 16" upper and have loaded four Pmags with four different loads.  We'll see what happens.

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4 minutes ago, ziebart said:

I tried to replace the extractor spring but it launched into orbit. Did manage to get the O ring in there and that seemed to help a lot

I had Wolff extra power extractor springs as I use them in my normal AR's. Use a small screwdriver to push the large end of the spring into the extractor, they shouldn't launch on you that way.

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I'll talk to CMMG on Monday.  I did shoot both barrels side-by-side with the newer carrier/bolt (came with the 8" barrel) moved to the older 16" barrel.  The problem, as expected, moved with the bolt/carrier.  The carriers are slightly different, the older version having the additional surface at the rear of the carrier to increase total bearing surface in the receiver.  I doubt that makes much of a difference.  So, the old setup works, the new parts not so much.

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CMMG is send a bunch of springs and a new extractor.  The extractor on the old bolt is a less beefy and the spring not as stiff as on the new bolt (with which I'm having an issue).  It if weren't for the issue with the 147gr Win PDX I'd say that the new design is tuned for factor loads, but the PDX FTE was on the first shot so no issue regarding bullet profile, etc.  The extractor spring difference is very apparent when I simple press and inert round into the breech face of the two bolts.  I might have expected the old design with a weaker extractor spring to be more susceptible to ejection issues?

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with a tip from Memphis Mechanic, I had a problem with the polymer helper plug in the OEM CMMG RDB extractor spring hardening...I used Memphis's suggestion and replaced the extractor spring with a heavy duty one from Bravo Company... no O ring or helper plug... 3 matches and about 100 trial shots it has been 100%... April match has been cancelled

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3 hours ago, Les Snyder said:

with a tip from Memphis Mechanic, I had a problem with the polymer helper plug in the OEM CMMG RDB extractor spring hardening...I used Memphis's suggestion and replaced the extractor spring with a heavy duty one from Bravo Company... no O ring or helper plug... 3 matches and about 100 trial shots it has been 100%... April match has been cancelled

Did the same, as highlighted in the thread I linked.  Has helped so far.

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17 minutes ago, RickT said:

I've order the BCM springs with little to loose.  The strange thing is that the new bolt with an obviously stiffer extractor spring is the one that only functions with factor ammo. 

 

Install the BCM spring by itself. No O-ring nor rubber stud needed.

 

You’ll probably find it helpful to use a C-clamp or pair of smooth jaw channel locks to compress that ultra stiff spring.

Edited by MemphisMechanic
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10 hours ago, MemphisMechanic said:

 

Install the BCM spring by itself. No O-ring nor rubber stud needed.

 

You’ll probably find it helpful to use a C-clamp or pair of smooth jaw channel locks to compress that ultra stiff spring.

I'm glad it was that simple of a fix.  Runs great now with my preferred H2-equivalent buffer system.

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I'm using CMMG bolt, barrel, lower, this is its second visit back to CMMG, and will be its third bolt. CMMG has been very good about taking the gun back, hopefully it is now fixed and will last well beyond a 1000 rounds. I've been through new extractors and new ejector springs also. Run factory Winchester or Federal 115gr

 

We updated your mag well and mag catch as we have made some design updates to those areas since your lower was shipped out. The mag catch modification allows the mag to sit a little bit higher to allow for a .40 S&W upper group to utilize the same lower as the 9mm.  This also requires a new mag catch as well.  The mag well  modification allows a little more clearance for Glock magazines. We have seen that Glock changed their mag specs after we released the 9mm lower. The newer spec magazines have clearance issues in our lowers causing feeding issues. This modification alleviates that issue. We also changed the design of our bolt carrier assembly. So we updated that as well.

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Here is what the repair label listed as work and parts

Update mag well and mag catch window to current spec

Replaced BCG and updated mag catch

Comment flat wire recoil spring won't run

standard carbine spring and buffer installed runs fine

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With new BCG, the flat wire spring might have made it over sprung. As CMMG fiddles with headspace, cam angles, lock lug angles, the recoil impulse changes noticeably. So mine will arrive Monday I'll look it over and do a couple of mag dumps

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Interesting to hear that they’re changing angles on the both teeth and such. I didn’t know that.

 

Then again, my gun is now extremely reliable and also the only Guard rifle I’ve ever seen in person. I haven’t had to get involved with their tech support.

 

I just fed it a 124 JHP defensive load I was working up. Went 1,420 FPS for 176 power factor. 😳
 

It just felt *slightly* hotter than the usual ammo I feed it, which was pretty awesome to discover. That round is a handful in handguns. 

 

Then had my fianceé run a hodgepodge of every leftover bullet I’ve loaded for 3 years which marginally failed the case gauge and got dumped in a “practice only” bin. 124 power factor LRN, coated TC, 147 FMJs at 140pf... it ate them all flawlessly with slightly mis-sized brass and OALs and powerfactors all over the map.

 

I’m *finally* really happy with the rifle. After a year of tuning & troubleshooting the build.

 

 

Edited by MemphisMechanic
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I've installed a BCM extractor spring and CMMG ejector spring and will try this out today.  Bryan (from CMMG) is also sending me a new bolt.  I'll post results as available.  It is baffling that the "old" bolt from my original 16" Guard has no issues.

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Final update: CMMG had also sent me an Extractor with spring.  Put this in the original bolt and the rifle ran 100% with five different loads including a very soft load that I run in my 9mm 1911.  When I receive the complete bolt assembly from CMMG I'll try that also, but even if it runs I'll be reluctant to let go of the now working bolt.  I can breath a sigh of relief.  Certainly CMMG was very supportive.

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@MoRivera The only things that you need to pay special attention to are (1) replacing CMMG’s underpowered extractor spring when it wears out in a few thousand rounds and (2) getting the magazine height dialed in for your lower and choice of magazine.

 

My gun could not run more flawlessly with OEM Glock mags, but if I tried to run ETS mags I’d break the feed lips off. This is simply a function of using a traditional “toothed gear” AR style bolt with a handgun magazine that’s got narrower feedlips than a 5.56 mag. Mags with all-plastic feedlips are wider than OEM ones with different height to the lips. So I elected to set my gun up to run with the most reliable option. That said? this is mostly due to my choice in aftermarket lower which holds the magazine differently than CMMG designed the bolt & barrel for.

 

Other than that, make sure your ejection port is large and find a buffer & spring combination your gun likes. That should be it. 👍
 

Edited by MemphisMechanic
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17 minutes ago, MemphisMechanic said:

@MoRivera The only things that you need to pay special attention to are (1) replacing CMMG’s underpowered extractor spring when it wears out in a few thousand rounds and (2) getting the magazine height dialed in for your lower and choice of magazine.

 

My gun could not run more flawlessly with OEM Glock mags, but if I tried to run ETS mags I’d break the feed lips off. This is simply a function of using a traditional “toothed gear” AR style bolt with a handgun magazine that’s got narrower feedlips than a 5.56 mag. Mags with all-plastic feedlips are wider than OEM ones with different height to the lips. So I elected to set my gun up to run with the most reliable option. That said? this is mostly due to my choice in aftermarket lower which holds the magazine differently than CMMG designed the bolt & barrel for.

 

Other than that, make sure your ejection port is large and find a buffer & spring combination your gun likes. That should be it. 👍
 

Yep, and thankfully I've replaced both the extractor and ejector spring with new xtra power units and it's been an improvement in reliability.  I use a CMMG Radial Delayed Blowback with a mil spec 5.56 lower and the CMMG 9-ARC Endo mags,  which run great in it.  I have two uppers that I built for it, one is more of a shorter 'pistol' length (but built as an 'other' for my state, hence the requirement for a vert. fore grip) with a pined/welded linear comp to extend the barrel length to 12.5"....

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This one I can just interchange the upper with a 5.65 one and use the same buffer and everything....an Armaspec Silent Captured H2-equivalent in my case.  The 5.56 upper on same lower......

 

WvAV7CJ.thumb.jpg.95e2a244266a2ce0ed6872e7e2ec218d.jpg

 

 

And another 8" barrel that I'll be using a Taccom barrel extension to make a 16" rifle length.  The one above has a receiver specifically for rifle calibers, hence wide enough for .45.  the rifle upper will use an Aero XL upper which has a wider port already.  Be using that one my PreBan lower that use with a Stern Glock Mag adapter of for now as a dedicated PCC rifle. Wit the CMMG upper, m I'd just remove the mag adapter.  Hopefully GTG.

 

Also, I just personally love the look of an AR mag more than the back-slanted Glock mag, so that's a bonus.

 

Edited by MoRivera
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Just to reiterate, the strong BCM extractor spring didn't do the trick so in my case the extractor, itself, appears to have been at fault.  If I start experiencing issues with the now working bolt assembly I'll definitely try the BCM extractor spring as the first fix.

 

Notwithstanding these issues the 8" SBR is a joy to shoot and much easier to transition than my full length upper, but then again I'm old.

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3 hours ago, RickT said:

Notwithstanding these issues the 8" SBR is a joy to shoot and much easier to transition than my full length upper, but then again I'm old.


I believe it. My CMMG 16” barrel has been turned down until it shed 8oz of weight on the muzzle half, and cut down to 13.5” for a pin & weld to hit 16.25” total.

 

It’s much lighter up front, and it made a huge difference in how the gun swings. Having NOTHING out there has got to be even better.

Edited by MemphisMechanic
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