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Posted: 8/11/2016 4:25:35 PM EDT
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I have a CMMG Mk3 that that's having issues cycling reliably. I bought the upper fully assembled from midway and got the lower from a local shop. LPK, stock, buffer, etc are all CMMG mk3 parts from CMMG website. Using Magpul 10 round LR/SR 308 Mags.
So Exactly like this here: https://www.cmmginc.com/shop/rifle-mk3-308-win/ - First time I took it out and fired 40 rounds, I had about 4 malfuctions where it would fire the round, but the empty case and new round would get jammed - 2nd time... Lubed it really good with tetra grease and went out and fired 40 rounds with no issues at all. - 3rd time.. Got a new optic for it and wanted to sight it in. Gun was cleaned and had light coat of CLP on bolt, etc. Fire a box of 20 rounds.. Couldnt get through more the 3-4 rounds before the jam would happen. - 4th time... Took home and dissambled bolt and cleaned everything really well. Coated with CLP. Brought four types of ammo (PMC, Federal hunting ammo, American Eagle, German Surplus stuff). Couldnt get through more than 3-4 rounds without a jam regardless of ammo. THEN, I decided to break it open at the range and really lube it up with Tetra grease like I did the second time out. Doing that, I was able to fire 15 rounds with no issue. Here's what the jam looks like... The empty case is still in the chamber and jamming up with the new round being stripped from the mag. http://i233.photobucket.com/albums/ee298/crazed1x/gats/9704D408-47A0-40DB-96A4-59C76437F49F_zpsecwsxmls.jpg |
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Had make two posts cause Im a noob...
Anyway.. I found two old threads where guys are have nearly identical problems with a CMMG and it seems like an adjustable gas block helped them out. http://www.ar15.com/forums/t_3_121/569850_New_CMMG_MK3_w__Issues___Ejection_Issues___Overgassing_Problem__Help_Appreciated_.html http://www.ar15.com/forums/t_3_121/568169_CMMG_308_ejection_problem_with_pics.html I wouldnt mind trying that out, but dont know exactly which one to get.. This is the barrel that the rifle has.. says ".936? Gas Journal" https://www.cmmginc.com/shop/barrel-sub-assm-18-0-ht-416ss-308-win/ So I guess my questions are: 1. Does this seem like a lubrication issue? Do these things really need THAT MUCH lube? 2. Can anyone recommend what adjustable gas block will fit on the rifle? |
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Quoted:
Extractor is letting go. Tony This. Try getting new extractor springs. Also, make sure your ejector has tight spring tension, and there is no debris. From the picture of the malfunction, my first assumption is the ejector. It doesn't look like is trying very hard. But very well could be the extractor slipping off the round prior to the ejector working. Spent round stays put, and gets slammed by the bcg chambering a new round. Strip the bcg completely. Clean with brake cleaner, get all the oil and grease off. Then relube very generously with motor oil. I don't like using any type of grease for the bcg. Only on threads. Traps too much of the burnt powder and other crud. |
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Ok thanks for the input.. Honestly it does seem like an extraction issue since the empty case is literally hanging around inside still.
Looks like replacement extractor and springs is around 40 bucks.. Ill contact CMMG and see if they can hook something up before I order parts out of pocket. |
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i have a MK3 3GR
and use nothing but handloads anything from 110 varmit bullets to 208 amax's had zero FTE the rifle runs perfect , i did machine a carrier weight for it and i runs with very little lube alittle on the rings and the key . i havent shot a factory round through the rifle just handloads . so i dont know how a factory round would perform . TS2 |
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Try at least 3 other (different) brands of magazines in this rifle.
As good as Magpul magazines are, some rifles are very particular in what works well. If it turns out to be the magazine (and I suspect it will be), compare the geometry of the lips and follower to your Magpul units, and you may be able to modify them to work better in your rifle. G. |
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Quoted:
That looks like a weak extractor to me. Looks like that might have been the issue. Emailed CMMG about the problem and sent them a bunch of pics of the malfunction and bolt. They sent me a new extractor, extractor pin, inner and Out Extractor springs, and two O-Rings. I could definitely tell a difference just putting the bolt back together. Before, I could slide the extractor pin in easily, but this time I had to use a little vice to compress everything so I could get the pin in. There is much more tension now. Fired off 60 rounds of various ammo tonight with no malfunctions.. So Ill call it fixed for now. BTW, CMMG great customer service to work with. They sent out the parts right away free of charge. |
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