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CMMG MK3 308 Lower with a DpMS Complete Upper


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New to this site just stumbled across it . I like it!!! Anyway i just built a 308 AR. DPMS Upper , slick sided, 18" bull barrel mated to a CMMG MK3 Lower. Got everything together, the mags(DPMS) fit, rifle seems to be  fine, however due to the lack of a forward assist, loading a round seemed to be hard, not like the AR 15s i Have built in the past. I did not have the upper milled for the g-3 mags, not sure what they are German or something.

Any suggestions, the mags are 20 rounds, it seemed to load better with a few round out of the mag. I hope to shoot it soon, but gotta get the boat ready for charter season.

Any input would be very very helpful. also I did buy some rounds that were on sale from cabelas. remans i think , they could be an issue.


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The lack of forward assist should have no effect on function. So what exactly is the issue? The rounds dont chamber completely? Not riding the charging handle is more critical on these guns then an AR-15. Lastly you say you did not have the upper milled. I believe that mod is for magazine to fit correctly. Perhaps even though they are fitting it's not the correct fit.

Just a few side comments. These .308 like to run with a lot of lube when new, dripping until they settle in. Has the headspace been checked? Ive attached a pdf of the upper mod for those who havent seen it. Definitely try different ammo

Thanks for signing up!!


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Ditto what 'Drew mentioned on the lube. I had my first failure-to-feeds on the range yesterday, and it only happened twice before I broke out the Rem-Oil and cured the problem by running slightly wet... I went through another 30 rounds after that with no problems whatsoever. Welcome to the forums, enjoy your stay. There are a lot of good people here, relax and post up some pics!!

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I tried the slightly wet method, cycled a full mag no issues. Great help guys. Now I just have to get out anb shoot the gyn.

I will try to get some pics up. The gun is the DPMS 18" bull barrel with slick side, CMMG MK# Lower, DPMS LPK, A2 tube, Aramlite Rifle buffer spring and one of Slashes xtraheavy buffers, And lastly a Magpul PRS Stock.

Just need the glass, a Trijacon AOGC 4X32 with red crosshairs and the Bi-pod.

I am thinking I will not machine the upper and If I have problems I will just change out the lowers, but I have to wait 30days in the republic of Maryland.

One thing about the CMMG lower , ther is a slight bit of play in the front pin area, but I think I can tighten that up a tad.


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So I'm sure I should know this but what are you guys meaning when you say runnin it wet?  I know lube but what exactly are you lubing that much?

I lock back the bolt in the open position, spray the inside of the receiver, close the bolt and spray the bolt lightly through the ejection port. With the bolt still closed, pull the REAR receiver pin and swivel the upper away slightly from the lower, and spray the back of the bolt from underneath, and finally spray the bottom of the bolt through the magazine well. I'm not going very heavy with the lube, just enough to run slightly wet.

Basically you just wanna make sure that the inside of the receiver and the corresponding surfaces of the bolt are lightly lubed.

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