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CMMG MK3 Problems

W

Warbone

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Minuteman
Oct 2, 2011
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Bought a CMMG MK3 a few months ago.
http://cmmginc.secure-mall.com/item/Mk3-18-Stainless-Steel-308-Rifle-1807
First trip to the range to break in the barrel with 2 boxes of federal 168g match ammo accuracy was between 1.5 and 2 MOA with flyers out too 4 inches. Gun was ejecting shells out about 1 oclock, typical for over gasing, also every 5th or so shell would fail to eject jamming gun. Installed a adjustable gas block and that corrected the ejectinmg proplem. Now after about 400 round of OCW trials and numerous factory loads i can sometime get 5 shot groups at about 1.2 inch, for longer ranges 200 to 300 yards accuracy is way bad.
Im thinking of either selling the rifle or switching to a differant barrel.
Ant tips or suggestions on what new barrel to try would be helpful as well as any tip for shooting ar10.
I have and tikka t3 scout that shoots under half inch all day long so ive been spoiled.
 
Re: CMMG MK3 Problems

sorry to hear your troubles, I was hoping these would be ok. I was really curious and played with one in the store, it looked nice.
I had a CMMG .223 ar that was awesome, should not have sold it
Thanks for sharing though to let others know

Good luck
 
Re: CMMG MK3 Problems

Dont get me wrong i do like the rifle, the upper and lower fit together really well, love the rail and its really light for a 308. Just not getting the accuracy i am used to. Any suggestions out that on a good barrel upgrade?
 
Re: CMMG MK3 Problems

Driving a 7.62 gasser is not like driving a bolt rifle or its smaller cousin the AR15. It will exaggerate any and all flaws in the fundamentals of marksmanship.

Give it more time and practice the fundamentals. Perhaps only 5-10 rounds at a time. Straight behind the rifle, follow through, trigger manipulation and keeping your shooting shoulder relaxed are all critical. Give it a few weeks to a month of perfect practice.
 
Re: CMMG MK3 Problems

I have been able to shoot my tikka t3 scout, and RRA ar15 varmint so well i didnt think the problem might be the shooter.

Still think i might switch barrels. Ant suggestions?

Anyone one out there with some pointers on shooting a 7.62 ar-10?
 
Re: CMMG MK3 Problems

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Warbone</div><div class="ubbcode-body"> Any suggestions?

Anyone one out there with some pointers on shooting a 7.62 ar-10? </div></div>

It's all fundamentals, do the same thing EVERY time
 
Re: CMMG MK3 Problems

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Warbone</div><div class="ubbcode-body">I have been able to shoot my tikka t3 scout, and RRA ar15 varmint so well i didnt think the problem might be the shooter.

Still think i might switch barrels. Ant suggestions?

Anyone one out there with some pointers on shooting a 7.62 ar-10? </div></div>Nope.

Bolt guns are forgiving to follow thru.

There are 3distinct recoil or movements to an Ar in .308 its more exaggerated. sign up for the online training there's material specific to your questions and it wont be a waste of $ like purchasing a new barrel will probably be. Its going to take some time to get consistent results like with your bolt guns or smaller ar15.
 
Re: CMMG MK3 Problems

What type of trigger is in it?

I have one as well... after after a trigger polishing job it got MUCH better results.
 
Re: CMMG MK3 Problems

also try just replacing the trigger spring from a jp reduced power kit. do a search here. GREATLY improved my stock MWS
 
Re: CMMG MK3 Problems

I put in a rock river match 2 stage trigger.
 
Re: CMMG MK3 Problems

Just a quick question. Did you get the regular Stainless Steel Barrel or their Cold Hammer Forged Barrel Rifle? I'm thinking about getting CMMG .308 Upper for my DPMS lower. I'm debating if the Cold Hammer Forged Barrel is worth the Extra $$$. very interest in how this thread turns out. Thanks in advance!
 
Re: CMMG MK3 Problems

Its the stainless steel barrel. After many hours of practice i am starting to get regular sub moa groups with this rifle. Shooting a AR10 is alot harder than a regular bolt action or ar15. Very happy with the gun now. Will probably replace the butt with a magpul PRS. If anyone buys one would recommend a adjustable gass block with it. Im using a PRI.
 
Re: CMMG MK3 Problems

Would over gassing cause pressure signs in brass? I have a CMMG SASS that I am having issus getting a load worked up for. Didn't know if that could be the problem.
 
Re: CMMG MK3 Problems

I don't know if any are out yet with the CHF barrels yet. They have a pretty nice looking one in they're store with a heavy spiral fluted barrel. If you like the heavy barrels.
 
Re: CMMG MK3 Problems

Well im getting very frustated, i think i find a good load. like 168g smk 41g varget get 5 shots group at about .75 moa. Reload 20 round clean gun and go back to range. Groups end up about 1.5 to 3 moa. Have found about 4-5 loads like this. Find a load reload some head back to range and groups suck.
I shot a friends ar10 and was able to get under 1 moa every time so i dont thinks its the shooter.
what could the problem be?
barrel?
Headspace?
upper?
im at a loss, ready to replace barrel or sale gun.
Any help out there.
 
Re: CMMG MK3 Problems

try to not clean it every 20 rounds....that may help. Also, why dont you try some different factory ammo?
 
Re: CMMG MK3 Problems

I have tried about 6 differant ammo types, best so far was the 168g FGMM.
Im wondering if the barrel is just tempermental, and if replacing it would help?
Maybe im just expecting to much out of the gun.
The tikka i have shoots 5shot groups under .75 inch all day long.
 
Re: CMMG MK3 Problems

I'm bumping this thread up to give the OP another take on the rifle. I have one. Seems to be reliable and quite accurate once you get the stock trigger out. I will add that the barrel does not like to be stripped of copper. My clean bore shots are 2 moa low and 1/2 moa left for about 10-15 shots on a clean bore. After that it comes back and is fine for me.

I'll also say that I'm not all that pleased with the velocities. I have not had it on a chrono yet, but it doesn't throw fed 168 gmm fast enough to get much past 800y at about 1000' asl. I have been very happy with accuracy out to 800y though.
 
Re: CMMG MK3 Problems

Im at a loss on this gun.
The other day i shot a .189 moa 3shot group single loading with this gun.
Right after that i loaded up three in the mag shot them, and ended up with a 1.57 moa group.
Shot three more single load bolt slaming, shot a .475 moa group.
I have no idea why this gun cant product groups under 1moa when autoloading from mag.

On a side not i cant submit post from my home computer, anyone that might know why.
 
Re: CMMG MK3 Problems

I can't say exactly what is going on, but I've recently climbed aboard the "stop over-cleaning" train. I used to clean after every range trip, now I clean when a good load starts to open up.

Second, I think if you're getting good groups with a load, then reloading the same exact load with different results...something with the reloading process could be to blame. I would start with the brass. Is it stretching on you? Are you bumping the shoulder back the necessary amount, not enough or too much? Are your flash holes clean? Are your mouths smooth and burr free?

Is each powder charge weighed? Is your scale calibrated?

Are your seating depths consistent? Is your neck tension where you want it? Crimping?

Besides your reloading techniques. The mechanics of the rifle could probably be considered constant. That leaves your shooting to blame. I'm still struggling with consistency with the AR10. I'm much better with much more time under it, but still not like some. I had a couple other guys try out my rifle. One being a high power shooter. Its like buying an electric guitar (without lessons), and taking it back to the shop because you can't "get it to play." The guitar playing guru picks it up and jams out some tune that makes you realize...its you...not the instrument. That's how I felt watching these guys use my AR10. It wasn't the gun or the ammo, it was the operator. The fact that I had no lessons or practice and expected to pick it up and start bug-holing, because I'm pretty good with my bolt action rifles, was completely unrealistic, and disappointing. But knowing that, I'm working on technique and its getting much better with practice. I suspect if you keep the rifle "as is" and put more time and rounds down range practicing good technique, you'll start shooting it consistently.
 
Re: CMMG MK3 Problems

im not sure how the reloading process got into this but, i always test accuracy with the same batch.
Next most people want to blame the shooter, but cant explain why i can post sub moa groups al day long when feeding one round at a time from mag with bolt slam vs having rounds autoloaded from mag and gun shooting 1.5 to 2.0 moa all the time.
 
Re: CMMG MK3 Problems

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Warbone</div><div class="ubbcode-body">
Next most people want to blame the shooter, but cant explain why i can post sub moa groups al day long when feeding one round at a time from mag with bolt slam vs having rounds autoloaded from mag and gun shooting 1.5 to 2.0 moa all the time. </div></div>

I have the CMMG 22" in .223. Dropped in a Geissele SSA-E, and it shoots sub-MOA fine. If I could ask, are you shooting over a bipod? If so, which one? I thought my FN .223 bolt gun had a crap barrel because it sure as hell had a crap trigger when it came out of the dealership - 14 lbs - but I had the trigger tuned and FN bench-tested the barrel and it grouped about 1/2 MOA or so. Sooooo, since it COULDN'T be ME, kept looking and lo and behold it was bipod hop on my Harris. Stopped using the Harris and it shoots fine, just needed more weight. I have no experience with .308 gassers but seems to me it's going to be a relatively light rifle, and with a gas gun you're going to have three distinct recoil impulses to manage. Anything that disturbs the vertical and horizontal components is going to spread the group.

Also you might check the flash hider to make sure it's aligned correctly. Finally, I'll betcha if all else fails CMMG will make it right. They're huge on customer support.
 
Re: CMMG MK3 Problems

any chance you aren't getting the neck tension tight enough on your reloads and possibly setting the projectile back a little when the round chambers?
 
Measure your ammo before and after auto loading into the chamber. Is there any difference in coal? Might be a neck tension issue. Also what about your scope? Change scopes and try again. I recently spent 250 reloads blaming the ammo or gun when the scope was the problem the entire time.
 
I had one of these rifles, when I got it home i noticed that the trigger was not resetting consistently, then not at all. Took it to the range and it started locking up, it was really bad on brass. Called them and sent the rifle back. They returned it quickly, but the upper was misaligned and continued to lock up.....I jumped ship and got my money back. The gun store quick selling these rifles because they were having so many complaints from competent customers.
 
If you are shooting from a bench try sand bags up front and the rear. This should help you get comfortable behind your rifle.

Leaving your barrel seasoned will improve your groups. Clean the chamber only with a 45 caliber brush wrapped with a patch, followed by a bore snake or rod just to sweep out the barrel. This will help with sticky chambers.

If your going for tinny groups try not to torque the grip left or right. I have a Spur mount with bubble level that exposes that flaw in my personal technique.

AR10s can be frustrating from a bench using a rest or bipod and punching paper. Get your gun dialed in, grab some sand bags and line up clay birds at 1/4 mile and see what you can do. You may find that your frustration will turn to joy. Good luck.

The CMMGs seem like nice rifles for the money. I first noticed them at the NRA show in STL and I check them out at Black Rifles in Columbua, MO when passing by.
 
Warbone said:
Bought a CMMG MK3 a few months ago.
http://cmmginc.secure-mall.com/item/Mk3-18-Stainless-Steel-308-Rifle-1807
First trip to the range to break in the barrel with 2 boxes of federal 168g match ammo accuracy was between 1.5 and 2 MOA with flyers out too 4 inches. Gun was ejecting shells out about 1 oclock, typical for over gasing, also every 5th or so shell would fail to eject jamming gun. Installed a adjustable gas block and that corrected the ejectinmg proplem. Now after about 400 round of OCW trials and numerous factory loads i can sometime get 5 shot groups at about 1.2 inch, for longer ranges 200 to 300 yards accuracy is way bad.
Im thinking of either selling the rifle or switching to a differant barrel.
Ant tips or suggestions on what new barrel to try would be helpful as well as any tip for shooting ar10.
I have and tikka t3 scout that shoots under half inch all day long so ive been spoiled.
Click to expand...

Your product link is dead - what model CMMG MK3 is this?
 
scatsob said:
The one with the issues in this thread is the 18" SS barreled one.
Click to expand...

Yes a dumb f with no input, High jack " got one of them on it's way I know it's going to shot, if not make it instead of crying.
 
enough said:
I'm bumping this thread up to give the OP another take on the rifle. I have one. Seems to be reliable and quite accurate once you get the stock trigger out. I will add that the barrel does not like to be stripped of copper. My clean bore shots are 2 moa low and 1/2 moa left for about 10-15 shots on a clean bore. After that it comes back and is fine for me.

I'll also say that I'm not all that pleased with the velocities. I have not had it on a chrono yet, but it doesn't throw fed 168 gmm fast enough to get much past 800y at about 1000' asl. I have been very happy with accuracy out to 800y though.
Click to expand...

The 168gr SMK was designed to be a 600yd bullet for matches. It just doesn't have much BC to get it past 800yds, even at 1000ft elevation. 8541 Tactical has an excellent video discussing the 168gr SMK. Up where I live, it flies great out to 1000yds, but not down near sea level. Another thing that can help stabilize it is a tighter twist like 1-10", vs. 1-12". If you want to shoot .308 at distance, go with the 175gr SMK, the 178gr Hornady, or shoot the 155gr Scenar, Berger, or Sierra MK really fast.

My go-to load for the .308 when I was still using a .30 bore (will probably never happen again) was the 155gr Scenar at 2820fps from Lapua brass and Vihtavuori N550 I think. Compare the 175gr SMK to the 155gr Scenar, with the 175gr at 2500fps, and the 155gr at 2820fps.

168gr Sierra Match King (SMK) at 1000 yards .308 Winchester - YouTube
 
Man this was a old thread someone brought back to life. (beating a dead horse).
The rifle had ejection issues that was fixed by a adjusable gas block. Imo brand new rifle should not have this issue with fgmm 168g ammo.
As far as accuracy its a 1.0-2.0 moa rifle at best, pretty good for the price. But i was spoiled by my tikka t3 scout.
Bought a DPMS-SASS 308, rifle shoots under 1 moa all day long and it has never had a single feed or jam issue. Couldnt be happier with this rifle.
Its not always the shooter on semi-auto rifles.
 
I purchased one of these rifles about two months ago and I have found it to be very accurate we were shooting golf balls put of a special target we made at 150 yards every time guess I just got a good one :cool:

ETA: I forgot to mention I did install a timney skeletonized trigger the day I bought it
 
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