Does copper fouling in rimfires cause degradation in accuracy when shooting lead target rounds? IE. Using cheap bulk copper plated for practise, then switching back to say SK or Eley Match.
Read Eagleye's post about the carbon ring.
The Brno No2 I recently traded off, would start to develop this ring around 100 shots. I used plated bullets in it quite often, simply because I had a case given to me a few years ago and wanted to use them up. The fellow that gave them to me wouldn't have appreciated me selling them off or trading them. They shot OK, but were "dirty" they left a lot of powder flakes in the bore and when I cleaned it I used regular Wipe Out for the initial soak. I was surprised when the first patch came out blue. That doesn't happen with waxed lead bullets. The carbon ring cleaned up with just the one pass.
I put some Wipe Out/Lead Out in to soak for 15 minutes and ran a clean patch. There was a bit of gray streaking on the patch, that appeared to be from the side edges of the rifling.
This rifle has a tight bore and chamber. It's extremely accurate with standard velocity CCI ammo.
The bore is close to perfect, with a bit of nitriding on the leade, but this is after 20K rounds, so it can be expected.
My Tikka T1x will show similar powder and lead residue after a couple of hundred rounds, with waxed lead bullets. It also has a tight chamber and bore. When adjusting the trigger pull, I tried to insert some commercial snap caps into the chamber, they wouldn't go in. They were tight in the BRNO No 2 as well but still useable. I had to make up some inserts with Delrin, so I could dry fire it, without fear of dimpling the chamber mouth.
I suspect, that the plated rimfire bullets I have will also foul the bore with the plating amalgam.
Those bullets are now relegated to my other, not so tight or accurate 22s.