Help with CMMG accuracy expectation

[knoxp11]

Hello,

I need some solid advice regarding my expectations and options to deal with my CMMG CBR .308 accuracy. As it sit now, I have a stock CMMG CBR .308, the 2013 version with SureFire Break. It has an ADM Recon mount, and Bushnell ERS 6-24. The upper and lower have a great fit, and the rifle has very good fit and finish.

I have had two range sessions; the first was involving my reloads, 175 gr SMK, CFE223, CCI200, and LC Brass. Accuracy was inconsistent, as in 2-3 inch groups at 100, no wind. I was using a rest, however not the best. Since these results were less than stellar, I decided for the next session to remove as many of the variables as I could. The second session, consisted of putting the rifle in a lead sled placed on a concrete bench, verified all mounts are secure, and leveled rifle. Focused on shooting technique, cheek weld, trigger pull, etc. I used Factory Hornady 168gr and 178gr match ammo. Set up chrono and recorded data. Accuracy improved from the first session, best group was 1.68” with the 175gr, the 168 showed a better 4 shot group at 1.1”, but had a flyer that put it at 2+ inches. The groups averaged 1.6"-2"+ over the session, I took my time, 5-10 minutes between shots. I have not cleaned the barrel since the initial inspection, I have not done a typical break-in, e.g.- shoot, clean, shoot clean.

I spoke with CMMG and they were helpful, but it looks like this is within the acceptable limits for this gun. I have checked the barrel and crown for obvious defects, but did not identify any.

So, where do I go?

I am open to getting a new barrel. If I did it would be an 18” in place of the current 16”, brand undecided, but options include Rainier Ultra Match, Mega, LW, Lilja, Fulton Armory. And sell the 16” to recoup some money. Heck CMMG only sells it for $264.00 new. If I go this route I will get a Syrac adj gas block and it will probably be a mid-length system.

I am also open to trying to get this barrel to produce consistent groups. Should I keep putting resources (money/time) into a hope? Try a break-in process, Tubbs FireLapping bullets, or just keep with the load development.

Any help is greatly appreciated. Also, I have pictures but no way to post if any one volunteers I can send them for posting.

 

[knoxp11]

Well I am in the process of a deep cleaning. I have never seen so many solid blue patches. I am on my 3rd round of wipe out. 1 hour test resulted in 3 patches soaked through. 2 hour soak same result, two solid patches, patched 2 more till dry, still shows residue. Applied third application, will wait 3-4 hours and see if it is any better.

I hope to shoot tomorrow and will try a break-in process. Hopefully better results in the near future. If the barrel doesn't improve, I believe I have narrowed down barrel selection to a 18" Rainier Ultra Match, or 18" Lothar Walter. Both medium contour with .750 gas block. The gas block will be a Syrac gen 2. Not sure if clamp or set screw.

Still looking for comments/recommendations.

Any help will be greatly appreciated.

 

[ORD]

If I missed it above, my apologies, but how many total rounds through the current barrel? Just seems like a WHOLE lot of copper fouling if you are just getting the rifle up and running.

Furthermore, at this point in time...break-in isn't going to help! What's done at this point is done. Sure, you can "season" the barrel with a couple fouling shots before you proceed with your accuracy testing, but in terms of smoothing things out, making cleaning easier, etc., forget about it! Furthermore, if CMMG's "guarantee" (if you want to call it that) for their rifles is only ~2MOA (or even 1.5MOA), I'd certainly be looking at a better barrel if your accuracy does not ultimately improve more with time. Both the barrels you are considering are proven performers and should be capable of delivering sub-MOA accuracy if you do your part. The other thing to consider is a possible trigger upgrade. While SOME of the CMMG rifles shipped with Geissele SSA triggers, some were shipped with just your basic, run-of-the-mill mil-spec which leaves a LOT to be desired. A quality, match trigger my be able to give you a bit more in terms of improving the accuracy of your rifle if you don't already have the Geissele upgraded trigger in place.

In any event...GOOD LUCK!

 

[tickled pink]

Have you ever done a "ladder test" with "your" rifle? If not I suggest you do so to find what your rifles accuracy load is. Each rifle can be different.

 

[BCP]

I bet if you did a load workup you'd get right at an inch or a bit better, assuming you have good shooting technique. I'm also unsure as to what it is that you were cleaning out of the barrel, just because the patches are blue doesn't mean that anything is necessarily coming out.

 

[ORD]

I'm also unsure as to what it is that you were cleaning out of the barrel, just because the patches are blue doesn't mean that anything is necessarily coming out.

He said above he's using Wipe Out...if that's the case and its the same product of that name that I'm familiar with, anything "blue" coming out on patches is indicative of copper fouling being removed as carbon build up is usually "tanish/brownish" in color if that's what's left in the bore. Either way...I'd still like to know how many rounds fired at this point that would leave that sort of copper fouling in the bore? Also, have you access to a bore scope? If so...might be time to break it out and have a gander on a "closer" level.

 

[knoxp11]

Guys thanks for all of the comments and suggestions. I have a few updates, but first answers to questions already asked.

ORD,

No worries on the delay, just glad to have the help. The round count as of the posting was 57. Probably like you, I was and am very surprised at the amount of copper fouling discovered. The 3rd soaking with wipe out seemed to do the trick, as it patched out with only one small patch of blue, then the rest were clean. As for the break-in, you are right, I guess I meant I hoped to remove the copper and hopefully continue to polish (shoot out) the rough spots. Also, the trigger in this rifle is a Geissele SSA. I don't have access to a bore scope, wish I did.

Tickled Pink,

I have not done a ladder test. I did attempt to complete the OCW process, however those results are the posted in the first post of this thread.

BCP,

I will continue to work on a load, but with the original result left me doubting, so that is why I paid for match ammo. The blue on the patch is from the reaction between copper and the wipeout product.


As for the update, I got to shoot today and the results were much more encouraging. I spent the first 10 rounds seasoning the barrel and verifying zero. The next 10 where shot by my family, and honestly they are just glad to hit the target, so not much data was validated here. I sat the rifle aside and let it cool, then shot another 5 shot string with my 175gr SMK hand loads, the result was a 2.4" scattered group. I let it cool 15 minutes and then proceeded to use 178gr Hornady Match, the 3 shot group was awful, approx 3 inches. After this I was pretty resigned that a new barrel was in my future.

Then I chose to switch to the 168gr Hornady Match, shot 2, wow these are looking different, so I took my time on the third, WOW that's a nice cloverleaf. I loaded two more and finished the group, it did open up after I changed my cheek weld, but still it would be this rifles first Sub 5 shot 1" group. AWESOME! Total size, 1.307 outside to outside, -.308 and BAM .999". I loaded more of my 175 SMK over 45gr of CFE and managed a 5 shot (1 called flyer) at 1.12". I changed back to the 168gr Hornady Match (final 3 shells) and managed a .60" three shot group.

At this point I decided to end my day, and I am feeling better about it. I really have no clue what got better. Could it be that I am between a sweet spot in the rifles fouling? Could it have started to smooth out the bore? Shoot maybe it was luck. I dunno, but I will re clean tomorrow to see how much fouling was accumulated over today's 35 rounds.

I am skeptical that the accuracy issue will return, I guess time will tell.

Again, thanks for the help.

 

[Cobracutter]

Yep, CBR is a fantastic rifle for the money, but its not a precision rifle. There were two main flaws with MK3 rifles, the trigger and the barrel. The trigger is addressed with the CBR with a SSA, but the barrel is still a rack grade.

Do yourself a favor, and spend the money on a quality barrel. Lija, Krieger, Bartlien. Skip the Rainer arms shit. Hell even a Criteron. Fulton Armory - Barrels

CBR + a Good barrel is a smoking deal for a quality .308 gas shooter. The reciever threads in mine were very good and did not need truing. Your not going to find a better .308 gasser for less than $2.5K

 

[knoxp11]

Updated results from the OP

Hey everyone! Sorry for the delayed response in posting updates. Since the last time I posted my baby girl was born 5 weeks early and spent 9 days in the NICU. Good news now is she is home everyone is stating to get to normal and as always God is treating us better than we deserve.

Update 1- I performed a secondary cleaning after the first major cleaning. The fouling removed was much less than the time I posted about before. I would guess 20% of the last time. Total rounds fired would have been the same as the first outing that resulted in the extremely fouled barrel.

Update 2- I decided to change my load recipe from 175 SMKs to 168 SMK loaded over R15. Long story short I believe I found a load that works. 42.1 grains of R15, 168SMK loaded to 2.800 OAL. I completed the OCW Method, one round at each target all the way through lowest to highest. I was only able to complete 4 of the 5 strings due to the range closing. The best load resulted in a average 2,375 FPS and a center to center 4 shot group of .461 inches.

I am a little concerned by the velocity, but honestly I really never shoot past 600 yards. I completed JBM ballistics on this round and it goes subsonic at 864 yards.

For now I am satisfied and I hope that I continue to prove out this load. The accuracy node for the other groups with a half grain over and over resulted in .80" 4 shot groups.

Any suggestions would and are greatly appreciated. Hope my pictures load!

 

[GH41]

What did you expect from CMMG? I wouldn't spend money trying to fix it. You got what you paid for. Be happy! GH

 

[Rade1MOA]

Don't expect any accuracy with a Cmmg .308. I was happy if I could get mine to fire two rounds in a row.

Sent from my XT1080 using Tapatalk

 

[Sterling Shooter]

OP,

I expect to hit where aimed, don't you? Think about it. Why did you buy your rifle? Certainly it was to serve a need. Does it fulfill the need? I doubt it's for LR, or benchrest competitons, so, for what shooting sports that are left, it would appear that your rifle would provide a very satisfying experience. Since your leisure time is a luxury, instead of fussing over hand loads and cleaning, focus on what skills you need to get the most from your rifle for what you are going to do with your rifle. Focusing on marksmanship overall will keep you interested in shooting since emphasis will be on you rather than the equipment.