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problems just popped up with the radial delayed bolt


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I've been shooting a CMMG RDS barrel and bolt in an home assembled carbine, not one of their dedicated lower/upper.. NFA Glock billet lower, Aero Precision upper... after some initial problems getting the magazine follower to clear the sharp locking lugs on extraction, it shot flawlessly for the last 6 months or so... last match I had multiple double feeds, which I attributed to the 40 round ETS mag with a trimmed follower nose.. I pulled the bolt apart and noticed that the elastic plug in the extractor spring was exceptionally hard, so replaced it with a BunaN "O" ring around the spring... testing Wednesday, with MagPul mags that clear without modification, I started having failure to extract problems... upon disassembly, noticed a bright spots on the nose of the extractor where it might have been bumping the barrel extension... the extractor nose appears to be below the face of the bolt.... will trim it a little... anyone else have any delayed symptoms like this... regards

Les  L747

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bwikel.. thanks for the reply... sorry, I didn't take any pics of the spot, and tried running a Swiss file across it which obliterated the mark... I have access to a fairly precise disc sander tomorrow, and will try to remove a small amount and ink it to see if I can see a contact spot...my original statement was slightly incorrect as I retained the plug initially and added the O ring when I got the failure to extract... have since removed the plug, and kept the O ring, the tension seems more reasonable, and the combination has always worked with my 5.56 carbines...I am wondering if the plunger ejector is allowing the short 9mm case to release from the bolt too early, and possibly bouncing around... for the brass that does eject, they end up about 10 ft at 4:00 ...I use an outside range on Wed where I am more free to play with the carbine

 

did you lower your mag catch shelf, or need to modify magazines?

 

Les

3 hours ago, Bwillis said:

 

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Same here. Had a guard run thousands pretty flwlessly. Then it began choking twice a mag, all kinds of hilarious malfunctions.

 

Put a BCM  in extra power extractor spring for a 5.56 into it (which is STOUT, with out any O rings)... it’s run flawlessly ever since.

 

And I’m running mine on a KE Arms ambi lower. I dropped the mag in the gun nearly 1/4” and turned an old ejector into a hook the sits on top of the feed lips so they can’t be overinserted on an open bolt.

Edited by MemphisMechanic
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Archangel.. no, just an upper I had on hand

 

Memphis... thanks for the reply,  I have contacted CMMG tech support and commented that others had problems with the plug... if the O ring does not work, will try the extra power spring...I tried lowering an NFA mag catch shelf about .070" and it would not strip a round, that is why I was modifying the nose of the follower.... the MagPul mags sit lower and do not interfere with the back edge of the bolt when it is retracted

 

all of a sudden in the match (naturally) weird stuff was happening... the blow back upper is sitting in the gun safe laughing ;)

 

 

Edited by Les Snyder
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Memphis... you may have already answered this, but at 72 I have serious case of CRS,... what lower do you use?

 

CMMG tech support (Brian) is sending me a new extractor... I ordered a couple of the BCM springs

 

I may have to look at the use of factory Glock magazines again...now that I have a little better understanding of the quirks of the sharp teeth on the bolt...I want the bolt to run free without hitting anything when it is cycled with an unloaded magazine inserted

Edited by Les Snyder
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  • 2 weeks later...

@Les Snyder just sent me a PM thanking me for suggesting the BCM extractor spring. I tried multiple things before my gun finally ran 110% reliably for 1,000rds without a fault. The extra power extractor spring was the change than finally fixed the gun.

 

Les just went to the range, and has found the same thing. His gun is running again.

 

To answer your question, I’m running a KE Arms Ambi glock-mag lower with a factory CMMG Guard upper.

 

Edited by MemphisMechanic
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 the forward portion of the ejection port was opened up slightly... used a 1/4" carbide cutter and removed the material just forward of the dust cover latch, to the depth of the dust cover recess... the 1/4" cutter gave a slightly more open front of the port, and removed the  corresponding bottom section to the receiver radius just above the dust cover rod ... a dovetail cutter cut a slight inside chamfer... will give it a try today... match Sunday... regards

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1 hour ago, Les Snyder said:

 the forward portion of the ejection port was opened up slightly... used a 1/4" carbide cutter and removed the material just forward of the dust cover latch, to the depth of the dust cover recess... the 1/4" cutter gave a slightly more open front of the port, and removed the  corresponding bottom section to the receiver radius just above the dust cover rod ... a dovetail cutter cut a slight inside chamfer... will give it a try today... match Sunday... regards

Can you take a pic of this?  Interested in how this looks.

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On 12/16/2019 at 10:06 PM, MemphisMechanic said:


Just the bare spring, yes. It’s heavy enough to be a PITA to install by itself, and getting anything else in there was proving to be impossibly tight.

 

 

I have a set of parallel, flat faced pliers.  They have proven to be invaluable working with guns.  I no longer drive pins in with a hammer and punch.  I press them in with the pliers.  The pliers made installing my BCM extractor spring very easy. (Thanks MM for the info on that.)  I imagine that you could use tape to protect parts with regular pliers.

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1 hour ago, BartCarter said:

 

I have a set of parallel, flat faced pliers.  They have proven to be invaluable working with guns.  I no longer drive pins in with a hammer and punch.  I press them in with the pliers.  The pliers made installing my BCM extractor spring very easy. (Thanks MM for the info on that.)  I imagine that you could use tape to protect parts with regular pliers.

 

Any chance you could please demonstrate how you do this? I picked up some BCM springs but man, it is super tough. I gave up trying to get that extractor pin in. Thank you!

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Anyone trying to install the extra power extractor spring make sure you aren't trying to use the original plug or an o-ring. With the larger diameter end of the spring down on the bolt you should be able to lay the extractor on top of it then compress it in the middle and insert the pin. 

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2 minutes ago, bwikel said:

Anyone trying to install the extra power extractor spring make sure you aren't trying to use the original plug or an o-ring. With the larger diameter end of the spring down on the bolt you should be able to lay the extractor on top of it then compress it in the middle and insert the pin. 

 

Thanks Brian. I'm not using the plug or o-ring. Just the BCM spring. 

Maybe I need to work on improving my grip strength, but man, I can't squeeze that extractor enough and get the pin all the way through.

Perhaps my technique is wrong.

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3 hours ago, SergioSF said:

 

Any chance you could please demonstrate how you do this? I picked up some BCM springs but man, it is super tough. I gave up trying to get that extractor pin in. Thank you!

 

I am just leaving to test my changes.  Will post a picture when I clean tonight. 😁

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