What happened to my barrel?

[jelenko]

After mounting a CBI medium palma on an R5 with a Pierce action, the first 6 shots were ~ 1/2 MOA. They quickly opened up to something over 2". The uncalled shots were mostly off on elevation. A few were centered, on call. The last time the CBI was mounted, it was shooting fine - including a couple groups all in the X ring on the MR31 with none of them touching the x ring.

The barrel has just over 1400 rounds through it. The borescope shows no fire cracking in the throat. There is a layer of carbon in the grooves. I couldn't see any burrs or scratches on the crown.

I remounted the barrel thinking I had made an error in mounting it. But, same results.

Changed barrels, nice 1/2 MOA groups.

Both barrels are 1:7 with Wylde chambers.

My question is what caused the CBI to stop shooting so quickly with just 1400 rounds on it? Any chance the barrel nut [got it from EABCO] is not true in some way? This is the first time I've used it. The one on the other barrel is an 'alternut' from Shilen - they can't be interchanged.

 

[CharlieNC]

To me both the recoil lug and barrel nut are suspect, as a few rounds of recoil causes the change. You can try hand lapping them, but replacement may be necessary.

 

[jelenko]

Thanks. I'll try the nut first.
Since I'm using the same recoil lug with the barrel that is performing well, would that indicate the lug is good to go?

 

[AckleymanII]

Try putting more torque on the barrel nut? I am guessing here of course.

 

[jelenko]

Try putting more torque on the barrel nut? I am guessing here of course.

Thanks. But, it's the same as on all my remage barrels - i.e., 40+ ft lbs - as measured by my calibrated arm.

 

[jelenko]

OK. Because the borescope was showing a layer of carbon in the first few inches that wasn't coming out with Boretech left over night, I JB'd it a bunch including several cycles with a patch wrapped around a brush. The amount of carbon is noticeably less and a patch starts easier.
I also changed barrel nuts and cleaned the mating surfaces of the recoil lug, the built in recoil lug and the 'face' of the receiver.

We'll see.

 

[Jdne5b]

what powder and bullet?

 

[jelenko]

Most of the 1400 rounds were with 8208 and H75's - nice accuracy.

For the episode a couple days ago - started with same load - got expected accuracy. Went to S77's/8208 with a load that has worked in my other barrels - started to open up. Then B80.5's/8208 - over 2".
Went back to the H75 load to confirm accuracy. Groups stayed just over 2".

 

[rjtfroggy]

In your first post you diagnosed the problem, just not the remedy.
You stated there was a layer of carbon in the barrel,
that will do it, clean the barrel down to bare metal and start over. Two or three fowlers and all should be good.
It is a 223 it should go another 1400 rounds as long as you treat it right.

 

[Badbob]

I basically had the same experience with 3 different CBI barrels. Who knows how diligent they are at chambering. All three shoot consistently in the 3s. Fine for hunting or PRS style competition but certainly not for BR. Consequently I'm selling them off and going back to a traditional shouldered and custom chambering by a qualified gunsmith using barrel makers with solid reputations. My suspicion is the barrel nut is just on adequate to center and hold the barrel square on the action but I don't know for sure. You're not alone.

 

[jelenko]

I basically had the same experience with 3 different CBI barrels. Who knows how diligent they are at chambering. All three shoot consistently in the 3s. Fine for hunting or PRS style competition but certainly not for BR. Consequently I'm selling them off and going back to a traditional shouldered and custom chambering by a qualified gunsmith using barrel makers with solid reputations. My suspicion is the barrel nut is just on adequate to center and hold the barrel square on the action but I don't know for sure. You're not alone.

I was wondering about the barrel nut also. But, when I took it off, it was pretty tight.

 

[rjtfroggy]

With a custom pre fit the nuts are fine. I doubt you or I can shoot the difference.

 

[DaveTooley]

OK. Because the borescope was showing a layer of carbon in the first few inches that wasn't coming out with Boretech left over night, I JB'd it a bunch including several cycles with a patch wrapped around a brush. The amount of carbon is noticeably less and a patch starts easier.
I also changed barrel nuts and cleaned the mating surfaces of the recoil lug, the built in recoil lug and the 'face' of the receiver.

We'll see.

Don't ever use a patch wrapped around a brush with abrasives. It turns the brush into a lap. Abrasives are a polish as much as anything and should be used on a patch only.

 

[jelenko]

Don't ever use a patch wrapped around a brush with abrasives. It turns the brush into a lap. Abrasives are a polish as much as anything and should be used on a patch only.

Dave - Interesting! Some people recommend using the patch around a brush.

What is the difference in effect to the barrel of a 'lap' vs just a patch?
Thanks!

 

[tobnpr]

I doubt it's the nut. Could be, but it wouldn't be my first suspect. If it were defective, it could definitely do it. I would loosen the nut, then lightly screw on by hand until it makes contact. Then check with the thinnest feeler gauge/shim stock to see if there's any gaps around the nut. If the receiver face is true, and the nut is true, there will be no gaps- the two surfaces will come into full contact without significant torque.

Carbon ring? Doubtful IMO that this is your problem. Not that it couldn't- and wouldn't- cause the accuracy issue. It's the fact that you said it was shooting fine when you pulled the barrel. I don't think that the carbon multiplied itself while the barrel was in storage. The same amount of carbon/fouling was present when you screwed that barrel back on (and immediately had accuracy problems) as when you took it off.

My radar is pointing me to the chassis. No experience with R5's, so I can't say how "possible" this could be.
Sounds like exactly what would happen with a receiver that's not fitted/bedded perfectly stress-free, and is removed and reinstalled with different action screw torque values.

JMO, YMMV. Good luck.

 

[Dusty Stevens]

Dave - Interesting! Some people recommend using the patch around a brush.

What is the difference in effect to the barrel of a 'lap' vs just a patch?
Thanks!

@FrankG has posted pics a few times of people that used abrasives on a brush. Its an eye opener. You can ruin a barrel before its ever even fired

 

[INTJ]

Dave - Interesting! Some people recommend using the patch around a brush.

What is the difference in effect to the barrel of a 'lap' vs just a patch?
Thanks!

This is a controversial topic. A lot of us used bronze brush wrapped patches with JB or Rem Bore Cleaner for years with very good results. On the other hand, few of us know as much about barrels and gunsmithing as @DaveTooley.

Many of the LR BR shooters I compete with like Iosso with the Iosso brand nylon brushes. Another competitor I know uses JB all the time like I used to. We tend to clean every 70-100 rounds and our barrels last about 1200 rounds for the 6 BRA. Most of the horror stories I hear about JB come from one or two highly publicized examples where excessive cleaning took place. I suspect these cases of excessive throat wear may be because the shooter wasn't getting all the abrasive compound cleaned out before shooting, but that is something I cannot know for sure.

In either a Precision Shooting or an Accurate Rifle magazine article several years ago, the author pointed out that JB bore paste created scratch marks finer than the 600 grit lapping compound scratch marks in the barrel. That author thus concluded that there was no issues with JB. Conversely, if JB was used an excessive amount then its possible that throat erosion could increase even with very fine polishing of the bore.

So I do not know the answer. I do know that I refuse to take the time that even the best chemical cleaners take. I also suspect the very aggressive chemical cleaners damage the barrel. Iosso is a mild abrasive and a chemical, is used with the hard nylon Iosso brand brushes, and that is what I am doing now. If my current barrel makes it 1000 rounds shooting well, I'll have no more concerns about Iosso.

Having said all that, even the most anti-JB on a bronze brush guys usually say it's okay for occasional use when you have very stubborn carbon fouling.

 

[DaveTooley]

I use Iosso in the shop just on a tight fitting patch. Flitz is in my traveling kit. I've seen bad things happen when a brass brush is involved.
Everything in moderation.

 

[FrankG]

You mean this picture......see attachment.

That 7mm barrel started having accuracy issues at 100 rounds. Picture is at 800 rounds. Fully polished +.002" out of the bore (tops of the lands) and the grooves now measure +.0015" bigger as well. Not to mention the bristles on the brush just beat up the lands. The lands/top of the bore because they stick up take the brunt of the beating. The lands are not much taller than the thickness of human hair to put it into perspective.

Just had another guy last week. Sent in a barrel because it's not shooting. Barrel has less than 200 rounds on it. Doesn't look like the attached picture below but when you look at the barrel it's really super shiny and the lands just look rounded at all the edges. I tried to give the rifle the benefit of the doubt. We retouched up the crown because we didn't like that either. Shot the gun last week. Guess what....smallest group I could muster was about 1.5" to 1.75". Most of the groups where 2"+.

No crispness to the edges of the lands at all. Shooter was using an abrasive as a cleaner and was aggressive with it. Everything looks really smooth and rounded over etc...just doesn't look normal.

I'll throw this in there as well. You can polish/clean the bore and make it too smooth. This will lead to a copper fouling situation. Once it starts you typically cannot get it to stop.

Week before this....got another barrel in. All copper fouled. The cleaner he was using didn't touch the copper at all. All we did was clean it like we normally do. Couldn't find anything wrong with it and it all looked normal. Sent it back to the guy for him to give it a try. He called yesterday and said it shoots like a million bucks. How did we clean it was the very next thing said.

So you have to clean and maintain it guys. Just be careful of how you do it.

Later, Frank

 

[okie]

You mean this picture......see attachment.

That 7mm barrel started having accuracy issues at 100 rounds. Picture is at 800 rounds. Fully polished +.002" out of the bore (tops of the lands) and the grooves now measure +.0015" bigger as well. Not to mention the bristles on the brush just beat up the lands. The lands/top of the bore because they stick up take the brunt of the beating. The lands are not much taller than the thickness of human hair to put it into perspective.

Just had another guy last week. Sent in a barrel because it's not shooting. Barrel has less than 200 rounds on it. Doesn't look like the attached picture below but when you look at the barrel it's really super shiny and the lands just look rounded at all the edges. I tried to give the rifle the benefit of the doubt. We retouched up the crown because we didn't like that either. Shot the gun last week. Guess what....smallest group I could muster was about 1.5" to 1.75". Most of the groups where 2"+.

No crispness to the edges of the lands at all. Shooter was using an abrasive as a cleaner and was aggressive with it. Everything looks really smooth and rounded over etc...just doesn't look normal.

I'll throw this in there as well. You can polish/clean the bore and make it too smooth. This will lead to a copper fouling situation. Once it starts you typically cannot get it to stop.

Week before this....got another barrel in. All copper fouled. The cleaner he was using didn't touch the copper at all. All we did was clean it like we normally do. Couldn't find anything wrong with it and it all looked normal. Sent it back to the guy for him to give it a try. He called yesterday and said it shoots like a million bucks. How did we clean it was the very next thing said.

So you have to clean and maintain it guys. Just be careful of how you do it.

Later, Frank

what are the diagonal lines that i am seeing??