1st AR - CMMG MK4 T

AR/M4 AR General Discussion
1

I am new to AR’s and new to this forum. I picked up a CMMG MK4 T at a good price and am really enjoying it so far. Been to the range three times since I got it 4 weeks ago. Rather than type all the details and post pics thought I would share a video about it. Only issue at the moment is the bolt is not locking back on empty mag with .223 loads, but locks back fine with 5.56. Shooting mostly 50 and 55 gr fmj ammo currently. Same issue with either 30 rnd pmag I have for it.
https://youtu.be/afKVZpfGSE8

Hope you enjoy the video and let me know if you have feedback on the bolt not locking back issue.

Dgunnut

2

I also have installed a BCM Gunfighter grip Mod 3. Already getting into the AR craziness of making it my own.
https://youtu.be/34XTNaSq9dA

Dgunnut

3

It’s malfunctioning out of the gate.

I’d send this back:
https://www.cmmginc.com/shop/rifle-mk4-t-5-56mm-2/

Get my $$$ back.
Buy one of the Colt’s or BCM’s from here:
http://www.gandrtactical.com/cgi-bin/commerce.cgi?display=home

Stick surplus cash in pocket or a nice light/sling, ammo, training;
And sleep better at night.

https://www.m4carbine.net/showthread.php?169739-bought-twice-finally-smiling

ETA
What good are all your accessories if it won’t shoot .223 ammo?

Why do you think it won’t shoot .223?

4

The OP’s gun is a POS and he sounds like Amsdorf in wanting us to click on his gun “review” video link so he can get advert $$$$ from youtube. No thanks.

5

Thanks for the warm welcome… I use videos to share info, not making any money off of it. I don’t consider my gun a POS. Bolt not locking back is not a major malfunction in my opinion. I hope there are more friendly people here to comment.

Dgunnut

6

I am not sure how I would have any money left if I bought a Colt or BCM. They were both a couple hundred more. I was looking for insight on what the bolt not locking back issue might be, not the immediate your gun is junk, you need to return it and buy the only two that ever work…

It shoots 223 fine, except the bolt not locking open on the last round.

Dgunnut

7

See Here—> http://www.gandrtactical.com/cgi-bin/commerce.cgi?preadd=action&key=6920

8

I paid $700 for the CMMG and it has a free float keymod rail. $850 for the colt plus 150 for keymod rail = $1000, which is a few hundred more according to my math.

Sent from my XT907 using Tapatalk 4

9

I made a mistake.

I see now that you stated on empty mag. I thought you stated it wouldn’t cycle a .223 round.

The rest, I stand behind.

EDIT

The website lists that AR at $1,050
That is what I was basing my post on.

10

And it sounds like you are going to have to drop some more money into it to get it to perform properly. The Colt/BCM would have performed properly in the first place. Just my 2 pennies though.

11

What .223 loads were you using? I have fired various .223 rounds at some point through my AR’s and they have always worked well. I would want to know why it didn’t. Was it the ammo or is it a defect?

12

Congrats on the purchase. Hope you really enjoy the AR-15 platform.

Seemed like all the criteria you used to decide on the CMMG makes sense to me. I think you’ll find that this forum is full of people who just have a ton of experience with this platform and it’s usually out of that experience that they find certain brands perform better for their needs than others.

That said, it sounds like you had a budget in mind, and the CMMG offered some upgrades that were important to you over other options. Personally I would have gone with a stripped down Colt and built up the upgrades over time, but as long as it functions correctly the CMMG should serve you well. There’s probably millions of people out there with CMMGs that work just fine.

As for the lock back issue, it’s pretty hard to diagnose on a forum without high-speed video or things like that. A couple things come to mind that it could be. First off, it could be the gun short stroking a little bit. Since it has a mid-length gas system (which is longer than the standard carbine), if the gas port isn’t opened up enough then there won’t be enough pressure in the system to get the bolt back far enough to lock it back. It may be getting back far enough to pick up a new round but not quite far enough to lock back on the mag. With full power 5.56 it’s giving it the extra juice it needs to do that. IF that’s the case, I’d probably recommend leaving it alone and shooting it for a few hundred rounds to “break it in”. Specifically what I mean by “breaking it in” is that the gas port will erode slightly over time and your buffer spring will wear in, which maybe combined will give it reliable operation with .223.

Another option (again, if this is the issue), is to play with your spring and buffer. Not sure what it ships with, but if it ships with an H buffer you can try a standard carbine buffer. Or, if it already has a carbine buffer, try a reduced power sprinco spring.

It could also be the mag. If the gun only came with one mag I’d definitely mark it and pick up a few more and see if you’re experiencing the same issue on all of them.

A few final suggestions:

  1. Pick up some FIREClean. Do the whole thing of completely stripping the bolt down, etc… and then lube it back up with FIREClean.
  2. When shooting your groups, I’m sure you already know this, but try at least 5 shot groups at 100.
  3. Since you have a 16" 1/7 barrel, I’d highly recommend playing with some heavier loads for accuracy. 77gr Mk 262 is always a good bet. There’s many manufacturers that make this load from IMI, CBC, Black Hills, etc… I think Federal might have a GMM 69gr load that would be good to try also. And then there’s some 75gr match stuff out there as well.
  4. Pick up a good quality light and sling for that bad boy!

Anyway, congrats on the purchase. Nice video walk through and happy shooting!

13

Thanks for the positive feedback. I like your idea of breaking it in before doing anything else. I am planning on doing just that. If I still have the bolt lock back issue after a few hundred rounds and after trying different mags I will try a different buffer or spring.

Dgunnut

14

The reason you got such an abrupt response is because of the audience on this forum. There are a lot of guys with a lot of experience and they hear people pipe in all the time with consumer grade rifles complaining about the problems they are having. It always goes the exact same way… Guy comes to forum with XYZ rifle, say they love it, but…they are have some problem. After 75 posts between the Op and the forum, the problem gets solved and it is almost always a poor quality part or poor/incorrect assembly. That is why people get huffy.

If you are having a problem with your brand new rifle, you should contact the retailer of the manufacturer first. A good manufacturer will do everything they can to correct your problem. IF they are a good manufacturer they should be very responsive. Good quality parts, assembly, and customer service is what you pay for when you buy a professional grade rifle as opposed to a consumer grade rifle.

Good luck

15

I might suggest you re-prioritize your upgrades. First get you malfunction issue resolved. It sucks to have a new gun with issues right out of the box, but with a little help it should be fixable.

I’ve had good luck with the TRS-25 (as a budget optic) . I would however upgrade the mount to a KAC unit for $50
http://shop.knightarmco.com/ProductDetails.aspx?ProductID=KM30779

I would then buy some good back up iron sights.

Get a sling.

Stuff like the grip and stock would come well down my list of upgrades.

16

I had the same issue with wolf .223. Cycled fine with anything else. If you have a buddy with an AR swap lowers. If his cycles, grab a different buffer spring. I built an über cheap rifle and the buffer spring was like an over powered spring. Bought an OEM colt buffer spring and had 0 issues after that.

The reason I bought a colt buffer spring was because it was probably closer to spec than the ATX kit I had installed.

Hope this helps and there’s a tough crowd here. I would like to add that buying a cheaper rifle because it already has a keymod handguard isn’t the best route IMHO. If I had it to do over, I would have bought a Colt 6720 out of the gate and left it as is and knock the bullshit off and spent more money on ammo and mags for training.

17

To say that it is not a major malfunction may lead you to overlook something being out of spec. I suggest you diagnose and fix before you do any further upgrades, and you should contact the manufacturer as well. Good luck with your new rifle sir.

18

How did you come to this conclusion in black? CMMG is a well known cheap (read entry gun).

C4

19

I agree. Ie owned several bottom tier weapons and have had substantially less than $600/each but I will say I selected my parts carefully. That doesn’t make it a colt or a bcm or dd or even the same quality. Whats being stated and challenged is the Cmmg is more of a mass produced recreational shooter than for someone who makes it more of their life.

The guys here take this seriously, it’s not a light hearted “maybe” hobby for most people here

20

Forgive me, I haven’t peered into your video, but, what Bolt Carrier Group do you have: semi-auto or full?

You will not fund much love with CMMG here, nor Bushmaster, DPMS (their .308s get some loving here), or other budget AR makers. There have been posts, and othe documented reasons most members here frown upon them.

Many reasons being the quality control of the companies, the materials they use, and even the quality of the steel. Yes, the Colts and BCMs cost more, but for us who buy them and depend on them either for competition, hunting, or our lives, we trusts these companies because of the quality of their gear.

All of my BCGs are from BCM. The one I primary run on my main weapon has gone 5,000-6,000 rounds malfunction free (doesn’t count ammo issues). I have ran my last upper 3,000 rounds with the same BCG without a cleaning and had no issues.

If you believe in the myth that the direct gas impingement system is unreliable, many members here, including myself, will dispell that myth in a heartbeat. It will depend on what quality parts you have, and also your determination if our points are sound to you. We’ve before that an “AR is an AR, you’re just buying the name” and again, we will point to posts and other documentation that states otherwise.

My advice to you is, plan on making your next AR now (definitely before the next year). Good parts are at low prices. Piece it together as you budget goes. In the end it will cost more than your CMMG, but reliability is worth the piece of mind.

High-point offers a lifetime warranty on their pistols. That’s nice and all, but a lifetime warranty isn’t going to fix your pistol in the middle of a fight.

ETA: Watched your video. You have the full auto BCG. Does CMMG MPI/HPI their bolts? If they do, is it lot/batch testing, or individual?

Might want to look into an extractor spring upgrade if you plan on keeping the BCG.