HELP! .....dedicated .22lr CMMG AR upper issues

[Tom E Gun]

So after wanting a short barrelled dedicated .22 upper for several years, I jumped at the chance to acquire a CMMG Mk4 PDW upper with a 9.2" barrel. I have only used it a few times and expected a certain amount of "breaking in" would be required. However the failures are getting worse not better as time goes on. At first i was blaming the CMMG mag, as the Black Dog mags were performing much better. Now I am getting a 10-20% failure rate with all the mags. I tried a variety of ammo including: Fed bulk, Fed auto match, CCI Blazer, Reminton yellow jacket and Rem subsonic. The only ammo that fed 10 rounds without a failure twice in a row was Rem subsonic. Almost every failure is the same: a round gets stuck half way between the mag and chamber at a 45 degree angle with the nose of the bullet jammed up against the top of the chamber and the bolt trying to bend the round in the middle, like this:

The bullets look like this:

Here is a pic of the CMMG collar and feed ramp:

I know it is very dirty in this picture, this is fresh from putting 250 rounds thru it at the range. Prior to this range trip it was thourghly cleaned and well lubricated.

So...does anyone with experience running a dedicated CMMG upper have any suggestions? I am wondering if the buffer tube may be allowing the entire bcg assembly, including the collar with the feed ramp, to move away from the chamber, rather than just the bolt. The lower is a RRA with 2 stage trigger and carbine bolt buffer. Another idea is that maybe the rounds are hanging up somehow on the feed ramp and it just needs a good polishing.
Suggetions are welcome...thanks

 

[drslav]

I had this happen with a pistol before. It was the feed ramp having the wrong angle. I won't say that's what's wrong with your gun for sure as it can be the mag to barrel alignment too. As in mag being too low. But I do think that polishing or refinishing the angle of the ramp could help.

 

[skoal]

I was just looking at these.....maybe ill hold off till other chime in

 

[Tom E Gun]

I had this happen with a pistol before. It was the feed ramp having the wrong angle. I won't say that's what's wrong with your gun for sure as it can be the mag to barrel alignment too. As in mag being too low. But I do think that polishing or refinishing the angle of the ramp could help.

Thanks I will try this...it can't make things any worse (hopefully)

 

[Tom E Gun]

I was just looking at these.....maybe ill hold off till other chime in

There is another CGN member who has one with a longer barrel, and he does not seem to be having the same issues,
see post #98 for his range report:
http://www.canadiangunnutz.com/forum/showthread.php/915092-22LR-AR-s-which-one/page10

 

[yohann160]

First thing you should do, unless you've already tried, is get a hold of a few minimags and see how those perform. If they fail, you know it isn't ammo related.

How many rounds are you loading in the magazines? Have you tried loading 1 or 2? Does it happen then?

Have you cleaned the magazines, are they dirty?

Does this happen when you manually cycle the action?

I've seen guys shaving bits off their mags' followers to get the correct angle to ensure feeding. Load an empty mag and check the angle of the feed lip vs the ramp, do the same with a loaded one. If the follower is out of spec, it might be rocking from side to side and might cause the issue.

Of course, make sure the feed ramp is clean and free of obstructions or defects. Polishing a 22 ramp is never gonna hurt.

 

[yohann160]

Oh and have you tried with and wihtout the bhoa with the cmng mags?

 

[Tom E Gun]

Thanks for the input Yohann;
This last trip to the range, I did not use the BHOA at all. I also loaded both the CMMG and BD mags with only 10 rounds at a time.
I will try to track down some mini mags as you suggested. I don't believe the mags were dirty, at all, but I will verify this.
It never occurred to me to cycle the rounds through manually...what a brilliant suggestion, I will try it and get back to you. I will also take a very close look at the follower angles.
Great suggestions, much appreciated.
TEG

 

[Tom E Gun]

I picked up 500 rounds of CCI mini mag this afternoon and 50 rounds of CCI SV, I will try them this weekend. I am also going to check the angle of the mag followers tonight and try cycling a few rounds manually. I will post results...


Here are some pics showing the different follower heights and angles of the 3 different types of mags:

I tried cycling mini mags manually with each type of mag, although I had a few failures to eject and a stove pipe, I did not have any of the failures like I described above where the bolt tries to bend the round in the middle. This seems promising....

 

[Beetle Outdoor Supply]

So...does anyone with experience running a dedicated CMMG upper have any suggestions? I am wondering if the buffer tube may be allowing the entire bcg assembly, including the collar with the feed ramp, to move away from the chamber, rather than just the bolt. The lower is a RRA with 2 stage trigger and carbine bolt buffer. Another idea is that maybe the rounds are hanging up somehow on the feed ramp and it just needs a good polishing.
Suggetions are welcome...thanks

The kit doesn't cycle like a normal bolt carrier, so the buffer/buffer tube really doesn't play a role other than to hold the kit in place with some forward pressure. Where a normal carrier would sit; the kit does all the functions of a bolt carrier and buffer while staying put as an assembly.
You should be able to cycle the kits bolt and the chamber adapter (or collar in your dedicated uppers case) should stay put between the carriers forks. My experience is that these kits be run well lubed to allow the bolt to cycle back and forth properly. Since your shooting .22's things will get gummed up fairly quick so I suggest taking a can of brake cleans with you to spray out the parts if somethings hanging up, then you can see if there's too much carbon buildup. As for lube I've always had good luck with a thin oil like break free clp. You might also have some buildup around the barrel extension and the collar causing it to stick back a bit (just a thought)
Have you consulted with your vendor?

 

[Tom E Gun]

Thanks for the input,

The kit doesn't cycle like a normal bolt carrier, so the buffer/buffer tube really doesn't play a role other than to hold the kit in place with some forward pressure. Where a normal carrier would sit; the kit does all the functions of a bolt carrier and buffer while staying put as an assembly.

The potential problem, I have noticed, is that the entire .22 BCG sometimes moves a small amount (2-3mm) so that the collar with the feed ramp is not in the correct position in relation to the chamber. I am not sure if this is because the buffer spring is not putting enough force on it to keep it in place, or is the detent on the collar, that matches up with a channel in the chamber tube,not functioning correctly?

Have you consulted with your vendor?

Not yet, but if I am still having problems after my next range trip, this will be my next move.

Cheers
TEG

 

[barsik]

many here have fingered the feedramp as the probable cause for the feed failures, and they may be correct, but take a hard look at the front of the bolt before you start removing metal. if the face of the bolt is rough, or the extractor has a sharp edge where the case rim slides past, this will also cause problems.

 

[yohann160]

Keep it clean and keep it wet. Try FireClean if you feel adventurous, it works miracles. CCI burns much cleaner so it will give you a chance.

 

[Tom E Gun]

many here have fingered the feedramp as the probable cause for the feed failures, and they may be correct, but take a hard look at the front of the bolt before you start removing metal. if the face of the bolt is rough, or the extractor has a sharp edge where the case rim slides past, this will also cause problems.

Thanks for the suggestion, I will look into this. I am going to visit a friend on the weekend who is a lot more knowledgeable than me about amateur gunsmithing. We will put our heads together and do some serious testing to see if we can get to the bottom of this. If not my next step will be to contact Questar who sold me the upper to discuss warranty/repair/exchange.

 

[yohann160]

Are any of those at weird angles against the feed ramp when they are inserted into the mag well?

I picked up 500 rounds of CCI mini mag this afternoon and 50 rounds of CCI SV, I will try them this weekend. I am also going to check the angle of the mag followers tonight and try cycling a few rounds manually. I will post results...


Here are some pics showing the different follower heights and angles of the 3 different types of mags:

I tried cycling mini mags manually with each type of mag, although I had a few failures to eject and a stove pipe, I did not have any of the failures like I described above where the bolt tries to bend the round in the middle. This seems promising....

 

[Tom E Gun]

Keep it clean and keep it wet. Try FireClean if you feel adventurous, it works miracles. CCI burns much cleaner so it will give you a chance.

I am sure those are all good suggestions. The annoying thing to me is that my old CMMG conversion bolt would feed anything, clean or dirty, wet or dry and did not need any breaking in or tinkering to work correctly. The only failures I experienced were a very occasional stovepipe or an empty casing getting stuck up high in the bottom groove of the charging handle. I guess I had expected that the dedicated upper would be just as reliable.

 

[Tom E Gun]

Are any of those at weird angles against the feed ramp when they are inserted into the mag well?

Well they are all at different angles, but it is hard to say which is correct. My gut instinct tells me the middle, moderate, angle looks the best. I intend to eliminate all other variables first, but eventually I think some of the followers may need to be modified to the best angle as you mentioned in post number 6.

 

[Tom E Gun]

July 13 UPDATE

My buddy Kim has diagnosed my problem, see photo below:

A broken firing pin spring; the firing pin was not retracting and therefore the protruding firing pin would keep the casing, of the new shell feeding out of the mag, from seating properly and would feed at a nose up angle. Then when the front of the bullet hit the ramp or chamber it would force the firing pin back and finally seat correctly - or - sometimes, cause the jam I was experiencing. This also explains why the problem did not appear the first few times I shot this upper. I will be contacting Questar/CMMG for some replacement springs.

Another issue we noticed, although I don't think it was contributing to the jam issue:

There is a small indentation at the back of the bolt face caused by the hammer. There was actually a significant burr at this spot that we smoothed off with a file. Question: is this normal? is it a bolt issue or a hammer issue? Here is the RRA 2 stage trigger hammer:

As you can see, the hammer has a small step in it and is wearing somewhat unevenly. Question: would it do any harm to smooth out the hammer and eliminate this little step?

 

[yohann160]

Glad you found the problem!

Your hammer is a rounded hammer, correct? CMMG says to avoid using a notched hammer with their 22LR rigs.

Here is mine for comparisson. There is a tiny kiss where the hammer strikes the bolt:

 

[Tom E Gun]

Thanks Yohann;

Mine has a very very slight notch. I would say the notch is only about .5-.75mm. I could easily file off the notch and smooth out the hammer, but I wonder if this would cause any issues with my LMT 5.56 upper ?