What would cause a barrel to be impossible to clean out copper fouling?
I have a Bergara 6.5CM barrel and no matter what solvent I use or the number of patches ran through it there is still blue on the patches.
It didn’t start until the barrel had about 750ish rounds through it. Before then it cleaned up like all my other barrels do. It’s been back to Bergara twice and both times they said it had extreme fouling but never gave me a reason why it couldn’t be cleaned.
I gave up on the barrel and got a new one just curious what caused it.

Pushing the velocity envelope?

Try one of the reverse plating / electronic cleaning methods if you want it all gone - have used successfully on really old bbls - sometimes of course you find bad stuff under the plating.

For really nasty stuff have used bore pastes.

Niether should be an issue on a match grade bbl (unless of course you are pushing the envelope)

Average speed was around 2850

My guess is that you have some heat cracking in the throat which is holding on to the copper.

I have never paid much attention to copper fouling.  If I were shooting benchrest and trying for ultra consistency, it would be an issue, but I have a stainless AR barrel that will shoot sub MOA with match loads and I can visibly see the copper on the lands at the muzzle.

When the fouling started the rifle went from shooting one moa groups to three-four moa groups. That was what brought the fouling to my attention.

Did you shoot it hot? That's what I'd expect from an abused barrel that was shot hot a lot and fire cracked the hell out of the throat. In any event, full stripping and bore scope inspection to follow.

Spill your load data too. Might be something there.

No it never got real hot, not any hotter than any of other precision rifle barrels.

The load that I ended up using was Hornady ELD Match 147gr with 42gr of RL17.

What cleaning rod and jag are you using? Some materials will continue to show the blue "copper" indicator with some chemicals giving a false positive.

Using a copper brush to scrub the bore with copper solvent will produce blue on the patch.

OP:  Did you shoot the rifle after cleaning it to see if accuracy had been restored or did you simply throw away a barrel because there was some blue on the patches?

Try Wipe-Out Brushless Bore Cleaner. Be sure to get the hose adapter that lets you come in from the chamber side (easier to use this way). Foam and leave 24 hours. Wipe out and refoam and leave for a couple hours. I'm pretty sure this will result in a copper less barrel that you'll need to refoul.

I tried that too, not much better.

What's it actually take to fuck up a barrel like that? I'm not seeing it being possible for even some of the dumbest shooters to be able to blast that many rounds through a bolt gun. Even then, wouldn't this be much more of an issue on the light barrel autoloaders?

Not calling you out, i just want to hear more/continue the discussion.

A 147 at 2850 from a 6.5CM? Yeah, you're running so hot dude, it's silly. You're 100fps over anything you should be able to get. Back off to 40 grains and work up a safe load. Also, you've done something bad to your barrel. Firecracking damage is possible but I'm betting that since you're running stupid high pressures means you're running stupid high heat as a consequence of Boyle's gas law which means you're vaporizing copper onto your bore and I doubt that firecracking is significant. I do bet that your throat is wasted. Back your load the hell off and I bet you don't see such a nasty time with fouling.

Just seeing color on a patch doesn't mean it's pulling a lot out, no matter how dark the color. You might have .2 grains of copper spread over your bore or you might have 2 full grains of copper laying like rivers of crud in all the firecracking. For fouling that heavy I'd pretty much fill the bore with Modern Spartan Systems Copper/Lead destroyer and let it soak a while. You have to understand that there's only so much copper a solvent can pick up and it's not a lot. Something like .2gr per tablespoon is what I'm seeing in 24hr soak tests.

Keep up the cleaning till it's clean and see if it'll shoot again. I'm personally betting you'll be buying another pipe and learning an expensive lesson.

Why Modern Spartan Systems and not Sweet's? Simple, I've been testing them both experimentally and MSS is more gentle to humans and steel while proving to be extremely effective at removing copper. It's about half as absorbent of copper per unit volume of solvent as Sweet's but there's no ammonia, it doesn't stink or burn skin and so far I haven't been able to get it to damage any kind of steel.

@59chevy

Might want to try some KG12. Looks like it's much stronger than sweets and the MSS. Clean the barrel with patches of degreaser, cap it, and fill with solvent. Let it sit for a day and clean it out with a flush of water.

A factory RPR barrel made to it to over 3000 rds before it needed to be replaced with 42grs of RL17 same with a Proof Research RPR barrel and the Criterion barrel on the rifle now is close 2000. I’ve never had any signs of over pressure or had the bolt be hard to open with that load.

I’ll dig the barrel out and try that soon. Thanks.

Have you tried JB Bore Paste?  Whatever it is, JB will get it out.

Using blue on the patches as an indicator the copper solvents are still working is deceptive if your rod and attachments have brass fittings.

@59chevy After four years of scrubbing, is it clean?

I started using Patch Out along with Accelerator and have had great success removing fouling and copper build up.

I also use JB Bore paste.