A question for the gunsmiths out there

[PanhandlePilgrim]

I noticed in the last few months that my 6mm BR was no longer living up to the accuracy it once held that was on par with the reputation of the cartridge. It is a varmint rifle and gun has about 1200 rounds down the tube which I know isn't much for this round, which is why I have one. I couldn't remember when the last time I cleaned it so I went ahead and ran some Bore Tech Carbon remover and it cleaned up pretty quick minus a small amount of copper. I ran a bore scope down the tube and found what appears to be pitting resembling a bug that ate through wood in numerous locations ranging from about 16-22" down the 26" long barrel. Anyone idea what could have caused this?

 

[Wrench]

Frank green jumped in on a thread on the hide a couple of years ago....it's corrosion.

 

[PanhandlePilgrim]

I'll see if I can dig it up. Thanks!

 

[Castle Rock]

That isn’t going to hurt the accuracy

 

[Vern400]

Same but mine is worse. I thought I took care of my rifle, but hunting in coastal salt marshes pitted my bore. But it's carbon steel, and it did take 34 years! I'm up to 1.5 moa from about 0.9

And sometimes when you clean them down the metal, they never come back if they're badly pitted. My college friend just re-barreled his 30-06 for the same reason. We both had about 4,000 shots down the tube. We have a really good gunsmith and he said there's no way in Hades that we wore those barrels out. It's rust.

I don't think the level of fitting I'm seeing in your barrel is going to affect your accuracy much. But you need to start oiling your barrel when you get done shooting.

At the end of this season I'm going to rebarrel.

 

[PanhandlePilgrim]

I might get some new brass and see if that helps but I cross posted this on Accurate shooter and I was also able to dig up the thread on Snipers Hide and all signs point to it is essentially barrel cancer. It's still shooting well, but not the benchrest level accuracy i was getting (this rifle consistently held 10 shot groups in the .3-.4 range and now it's closer to a minute.)

 

[TaperPin]

I noticed in the last few months that my 6mm BR was no longer living up to the accuracy it once held that was on par with the reputation of the cartridge. It is a varmint rifle and gun has about 1200 rounds down the tube which I know isn't much for this round, which is why I have one. I couldn't remember when the last time I cleaned it so I went ahead and ran some Bore Tech Carbon remover and it cleaned up pretty quick minus a small amount of copper. I ran a bore scope down the tube and found what appears to be pitting resembling a bug that ate through wood in numerous locations ranging from about 16-22" down the 26" long barrel. Anyone idea what could have caused this?
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That’s what it is, but it’s sure a weird way for corrosion to form, rather than simple pits. Is it blued or stainless?

 

[Weldor]

Have you bore scoped it before? JMHO but could they be forging voids.

 

[Vern400]

I might get some new brass and see if that helps but I cross posted this on Accurate shooter and I was also able to dig up the thread on Snipers Hide and all signs point to it is essentially barrel cancer. It's still shooting well, but not the benchrest level accuracy i was getting (this rifle consistently held 10 shot groups in the .3-.4 range and now it's closer to a minute.)

One thing I learned. A pitted barrel may take more shots to "come back in" after a good cleaning. The fouling fills and smooths the pits.
That's part of what you get out of a premium barrel. A few shots to "blow it's nose" and you're grouping again.

Start clean and fire a single group till they start punching one hole. THEN shoot a group after cooling it good. My best rifle comes in with 3 shots. My savage 223 takes 6, but then it shoots 0.75 for the next 60~80. Rough but good barrel. My numbers are for 6+ shot groups and there ARE NO flyers. Ever. Every shot counts.

 

[khuber84]

Have you re-tuned the load? Sub half moa 10 shot groups is great, but as the throat wears it'll change your jump length, psi. I'd take your load and seat it 0.030 and 0.020 longer base to ogive and shoot groups. Is the velocity still the same? Throat erosion will also lower velocity as of drops pressure. You may need add another 0.15 to 0.3 grains of powder. My friend shoots a 6br that has 3k rounds on it and still shoots half minute 10 shot groups with 107smk.

 

[MThuntr]

I've seen these patterns in barrels before but only in low quality stuff from Bear Creak Arsenal. That's my only experience with those patterns. Things sometimes slip through the QC process but probably not on a 6BR build