CMMG MK4 PDW, 300 Blk upper - good, bad and/or ugly?

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Doc S
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CMMG MK4 PDW, 300 Blk upper - good, bad and/or ugly?

Post by Doc S » Mon Jul 18, 2016 4:36 pm

I'm looking at possibly picking up a CMMG MK4 PDW upper, 300 Blackout with an 8" barrel and was wondering if anyone had any experience with this upper. It'll most likely get paired with a CMMG MK4 lower, but I'm keeping my options open on that one. The only reason I'm doing it separately is I can get a wicked price on the upper through a military-only site, but they can't do lowers or pistols/rifles since it's internet only. It will be a pistol, since I'm not interested in giving the gov't another $200 and eight months of my time for an SBR. Figure if SHTF, nobody's gonna care if I shoulder a pistol brace.

Any opinions are welcome. Thanks!
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Re: CMMG MK4 PDW, 300 Blk upper - good, bad and/or ugly?

Post by BlogSarge » Mon Jul 18, 2016 5:22 pm

I don't have the upper, but I do have my own build that uses the 8" CMMG barrel. I just got back from the range shooting in fact.

At 50yds with an EOTech it groups better than my eyes can see. I was getting about an inch groups, but then my eyes are pretty well hosed and the red dot sight looks like a cotton ball with spikes sticking out of it, so I never really know where exactly I am aiming...

Screwing my 762-SDN-6 onto my Brakeout2.0, I get about 1" POI shift down. POI shift is consistent and repeatable.

When I worked at the gun shop we sold quite a few CMMG items and they seem to be well received. If the price is right, grab it. If you don't like it you can always sell it.

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Re: CMMG MK4 PDW, 300 Blk upper - good, bad and/or ugly?

Post by danield » Mon Jul 18, 2016 5:30 pm

Cant speak to the upper but my 8 inch CMMG barrel is a great barrel. Groups great. I couldnt be happier with it.

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Re: CMMG MK4 PDW, 300 Blk upper - good, bad and/or ugly?

Post by RAINS » Mon Aug 01, 2016 6:58 pm

I have a stock 8' CMMG MK4 PDW upper. It runs fine without or without my suppressor. It's more accurate than I can shoot it. It will cycle UMC subs without a can and lock back. It may or may not cycle with weaker subs and no can. She also likes the very hot H-day custom 110g v-max load.
I feel that the upper is a good value. The rail is actually pretty light and usable. The barrel is a profile that actually works with a shortie. The only bit I don't like is the built into the rail QD sling swivels. They are aluminum and will wear out quickly with hard use. CMMG has great service as well.
I will say this though unless you are going to suppress it don't bother with an 8' barrel. Get a longer one. By the way the only ammo the gun hates is the Fochcchi 150g! R

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CMMG MK4 PDW 300 Blk upper good bad and/or ugly

Post by FrankKeymn » Sat Apr 06, 2019 12:34 pm

Re: The Good, The Bad, The Ugly: Goffin's Cockatoos.

Thanks for this. I have more or less decided that my next and final larger bird will be a Goffins when the time is right. It's good to know what I have to prepare for.

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