CMMG upper...help

[green grunt]

Hello to all.....got a small problem with my CMMG complete upper , just a bunch of faliure to fire with diff. types of ammo , looks like light strikes..... ??

ammo: fed 40grns , cci hp , and rem golden
mags : black dog 10 rds (4)
lower : box stock AR15 lower , works great with a 5.56 upper in place

I could not get thru a 10 rd mag with out having at least 4-5 failure to fire

the fed 40grs bullets were real bad , I went thru a few mags and not even one round would fire ! (put them in my handgun and all went bang , not the ammo)

the rem golden bullets were the best of the bunch , with maybe 8 out of ten would fire fine

the cci velocitors were not much better then the fed ammo !

when it went bang....the groups were good at 25yrds

I got so mad at it ..I almost went to the truck to grag a pair of nippers to cut a coil or 2 off the firing pin spring....thought I better ask a few others first if they have had the same trouble before cutting on it !

total rounds 1st trip out...about 80 , and all the same trouble , break in ?

2nd trip (today) about 300+ rounds , should be broke in by now ?

help / input would be great.....thanks in advance...

Semper Fi
(can't get the darn photo thing to work...sorry)

[ejhc11]

Maybe a new stronger hammer spring, also you don't have a polymer lower do ya?

Don't mess w/the CMMG upper - its got a lifetime warranty. Contact Dave aka Shadow65 here on Calguns, he can assist you if you need to send it in or troubleshoot the system.

I owned two and them been flawless.

[green grunt]

Lower is a SOG , with a DPMS lpk , good solid lower with stock factory parts , maybe a stronger hammer spring ? it works fine with a 5.56 upper...

may have to send it in...don't know yet , would 300-400 round count be good for a break in ?

[paintballdad]

I had the same problem with my CCMG upper over a year ago. Shot Federal, Winchester and Fiocchi .22LR ammo with similar results.
Shadow65 recommends still using a buffer and action spring even though it is not needed with a 22 upper. I also recommend using a Taccom Pressure Plug.
If the problem persists then send it back to CMMG. They might need to buzz the chamber and check the firing pin.

[green grunt]

Thanks for the input....using a h-buffer with stock carbine spring

what is a Taccom plug ?

did yours settle down or did it need a bit of work ?

[nrakid88]

Thats a bummer man. i cant remember the last malfunction mine had, and i shoot several thousand rounds a year through it

[tanakasan]

+1 Taccom pressure plug. Get the reliability kit with firing pin.

Robert

[paintballdad]

Here's the linK to the Pressure Plug.

I sent my upper back to CMMG for them to check out. According to the repair order, the light strike misfires was due to the cartridge was not seating all the way in the chamber. They "buzzed" the chamber to smooth it out and cleaned & checked the firing pin. I ordered and installed the pressure plug as insurance against light strike misfires. The upper has been 100% reliable since.

[green grunt]

Thanks much for the link

when I pull the CH all the way back hard... I get a bit of movement of the front collier (1/8" maybe)....the pressure plug may be the fix I need...

[pennys dad]

Hi

I had the same issue a few weeks back, I was lucky to have 2 other uppers handy.
I change uppers, mags, entire bolt assemblies, springs, firing pins.
I also rechecked my lower assembly and buffer spring.

End result was firing pin. Switching the pin solved 99% of all light strikes.
I changed the firing pin to one that was consistent and the rifle fired.
I still get one light strike every 50 to 100 so I feel additionally a stiffer buffer spring and H2 buffer are needed for adjustable stocks but for the A2 stock the defaults work fine.

[onegtalon]

Taccom reliability kit is your best bet. For one for my CMMG dedicated and all the problems went away.


Sent from my iPhone
OneGtalon

[sdallace]

Make sure to put a tiny drop of lube in the extractor pin? Mine wasn't closing completely*cuz crud got into it. So it would have light strikes

[green grunt]

thanks to all for the help and info .

[shadow65]

Most likely is CMMG has too much head space on the bolt.
This is nothing new.
The TACCOM Reliability Kit will solve a lot of issues with light strikes and feeding.
The TACCOM Firing pin is slightly longer, comes with shims to adjust length, and is has a smaller, angled tip for more reliable ignition. It's also hardened so much less likely to break.
The Extreme extractor has a better angle on it and gives better, more consistent extraction to make upo for the excessive head space on the bolt.
The Pressure Plug keeps pressure against the rear of the action to give 0 movement under recoil which can absorb energy from the hammer strike resulting in light strikes.
It does need to be used with a buffer and spring.
This is the best up grade I have tested for solving the Atchison type conversions issues.
I have one if you need it.
Dave N

[green grunt]

Thank You Sir , I already ordered a complete kit , good to know the info given by others is spot on , its a nice upper and I like how it shoots (good groups at 25yds!)

looking forward to giving it a good run when the parts show up.

Thanks to all for the help/info..............range report coming soon...