So I got a chance to play with my 4.5 inch barrel and ss bolt/collar yesterday. I only put 30 rounds through it. I was using a black dog mag. Suppressed too.

First 5 shots were rem green box. Well 3 out of 5 jammed, and they jammed during feeding. I figure that was an ammo issue, based on the fact that CMMG says fed bulk pack worked best. So I switch to fed bulk. loaded up 25 rounds. First ten cycled without issue, and I was quite happy. Out of the next 15, I had around 7 stoppages, and I noticed they were good rounds. The primer struck them, but they didn't go off. The first two I just figured bad ammo, but it kept happening. Bang, click, rerack, bang, click, etc. All were struck primers, however they seemed light. I'm thinking that the primer just wasn't hitting them hard enough. The last round didn't go off, nor did it want to eject. I kept pulling the bolt back and letting it go, hoping the extractor would grab it and pull it out. Nope. When I got it out finally, I noticed the rim was all chewed up.

Thoughts or ideas?

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Ok, I switched out the trigger to a regular stock trigger. I loaded up 15 rounds, and got 6 failures to fire. bang, click, bang, click, etc.

So its not the trigger. I'm getting really light primer strikes.

Here is a picture of some brass. The right 2 are still live rounds, and I tried to fire them several times. Perhaps bad rounds on those, I'm not sure, but with 50% failure rate it could just be the gun.



Here are pictures of the bolt in the upper showing the breech and collar. I have the bolt pushed in as far as it will go.

I've had the same issue with a couple of CMMG left hand dedicated bolts.  CCI Standard and CCI MiniMag.

The Timney trigger (4lb unit) may have caused some but none of the strikes were light.  Runs my Spikes, Air Force and multiple Ciener units without problems.

Regular trigger group had one CMMG  running fine but the other continued to have failures to fire.

The round that never went off - I've had the same thing happen once or twice.  All good strikes but no ignition. The rim was chewed and distorted to heck by all the FP strikes.

Almost all of the misfires go off on the second try.

Check the backing plate on the frame of the CMMG unit.  Both my CMMG LH units had cracked/loose backing plates - and no I don't have old or shortened recoil springs.

Friend is welding them for me.  He is a retired PHNSY welder - excellent welder - he says the original welds were poorly done.  Kinda like they tacked the corners and "smeared" the rest to make it look like it was fully welded.

Here's a few pics of the two cracked plates - top one actually moves when grabbed and wiggled:



YMMV

What trigger are you using?? Anything 3.5# and under and you will have issues.

It's not probably feeding the remmy ammo due to the rim thickness and the CMMG set up.

I'll give you the poor man's approach......polish up the 'inside' of the extractor and 'sharpen' your firing pin

Tim

Its got a RRA two stage in the lower. It's my SBR. If I have to switch it out then I will.

I'm about to just buy a taccom firing pin and be done with it but I'm looking at the poor man's approach

It sounds like a tight chamber.  I would "Buzz" Chamber try to help if not contact CMMG and see what they say.  

If you are going to buy parts get the TACCOM reliability kit.  It is worth every penny.

MAHA

Ok. I buzzed the chamber and polished the feed ramp. Then I loaded up 15 rounds. First round fired then the second failed to fire. Light primer strike. Got of two more then again a failure to fire. That one failed to eject as well when I pulled the charging handle back then let it go and tried again. No eject. I jimmied it out and got off  ten without issue. Then had another light primer strike. Fired again then another. So out of 15 rounds I had 4 failures to fire and one didn't eject.

I don't know what else to do except put in a taccom firing pin.

Do you have the older notched hammer?

Dave N

No it's a newer rounded model. Got it a few years ago.

If there is any play with the bolt inside the upper this can lead to failure to fire and why a lot of people use the pressure plug.  I think I read where CMMG had several bolts get out that had to deep of breach face cut which could cause failure to fire.  There have also been reported problems with firing pins and firing pin springs.  I'd drift out the roll pin and inspect both.    I hope you sort it out but if I were guessing I don't think the problem is with the RRA hammer.

yeah I'm going to mess with it to see if the bolt moves with I pull on the charging handle. If I dont notice anything, I'm going to try it out on another lower with a regular FCG and see how it cycles. I'm reading a lot of things about failures to fire with the 2 stage trigger

Seems to be an abundance of CMMG BCG problems lately.
I'd say time to check the specs.

Dave N

update at the top

I think a abundance of CMMG problems is a little strong. I read here alot and do not see many at all. Every product no matter what can have a problem occasionally. Ours both run flawless but they are few years old..

There has to be a simple solution here. Sure wish I could see it in person..Have you called CMMG at all?

Yes I called them a short time after I updated this. I was told to check the ball detent in the collar. He said they had one come in like that last week, just a bad spring, and it causes the bolt to move a few thousanths of an inch, and thus it wont seat right on the barrel. I'm going to check it out when I get home.

I was very impressed with the customer service. I asked for tech support, and it wasn't a put you on hold thing. The receptionist put the phone down and went and grabbed him. He then started the troubleshooting steps. It was nice talking to someone that doesn't treat you like you're a moron. He was very much about helping me, and was very into what could be the issue.

Great, I hope you can get it figured. They have always treated me very well.

Get a Taccom pressure plug to hold the bolt in place.

I just wanted to add that I'm impressed with CMMG technical support / customer service.