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CMMG Guard tuning (9mm)

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On 9/25/2018 at 11:09 PM, cking said:

Update of new BCG. CMMG put a new BCG in my Guard, it runs! However the recoil impulse is noticeable harsher even with 223 flatwire and hyd buffer. Which makes me think they changed the angle of the locking lugs to leave more momentum in the BCG. So now I'll move on to testing a 308 spring and probably a 308 flat wire.

 

Did you get to test this out yet?  I had my first failure to eject in a match this weekend.  I have at least 6,000 rounds through my Guard.  I am going to disassemble my bolt and give it a good cleaning.  I admit that I have not disassembled the extractor or ejector for cleaning before, hope that is all it is.

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Does anyone have the specs of the ejection port of an actual Guard upper? I was using a .458 upper, but I'm building a 'red' one for my wife and using an anodized 223 upper and want to dremel/file out as little as possible. Seems like .458 spec up front and then just some light removal of the bottom on the rear 1/2 and nothing up top?

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6 hours ago, Acer2428 said:

Does anyone have the specs of the ejection port of an actual Guard upper? I was using a .458 upper, but I'm building a 'red' one for my wife and using an anodized 223 upper and want to dremel/file out as little as possible. Seems like .458 spec up front and then just some light removal of the bottom on the rear 1/2 and nothing up top?

 

Here’s mine. I just opened up the front half of the port as wide as makes any kind of sense. Then a pinch more

 

458 socom port? Nah. Keep going.

 

(Click the photo and swipe for a better view)

 

 

Edited by MemphisMechanic

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I saw yours in my search and it looks great. My only concern is I'm not refinishing once it's done. Does the rear of the ejection port actually matter? I've never really looked to see where the brass/base is when it's ejected. I only mentioned .458 since that's what I was using and it had so far worked 100%.

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22 hours ago, Acer2428 said:

Does anyone have the specs of the ejection port of an actual Guard upper? I was using a .458 upper, but I'm building a 'red' one for my wife and using an anodized 223 upper and want to dremel/file out as little as possible. Seems like .458 spec up front and then just some light removal of the bottom on the rear 1/2 and nothing up top?

 

I milled the top front half 0.038" and the entire length of the bottom 0.110".

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On 10/15/2018 at 10:37 AM, BartCarter said:

 

...  I had my first failure to eject in a match this weekend.  I have at least 6,000 rounds through my Guard.  I am going to disassemble my bolt and give it a good cleaning.  I admit that I have not disassembled the extractor or ejector for cleaning before, hope that is all it is.

 

Well, shame on me.  My bolt really needed a thorough cleaning.  Ran a match last night and it was flawless.  So, more bolt cleaning for me.  😝

 

Also, I did call CMMG to see if they had advice on this.  They are sending me their updated ejector and buffer springs.  I asked and the new buffer spring for 9mm Guard is now a .556 carbine spring. 

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15 minutes ago, tha1000 said:

 

@MemphisMechanic  that build is nuts.  I like the crab trap that you turned into a hand guard.

 

That’s about $300 worth of crab trap from Brigand arms. Including the barrel nut, it’s just over a quarter of a pound. Between that and having the barrel turned down... now I pick up everyone else’s rifle and think it’s a heavy pig up front. 😂

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Just now, MemphisMechanic said:

 

That’s about $300 worth of crab trap from Brigand arms. Including the barrel nut, it’s just over a quarter of a pound. Between that and having the barrel turned down... now I pick up everyone else’s rifle and think it’s a heavy pig up front. 😂

 

I bet.  

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