True... When I first got into handgun shooting (1986) I'd owned some kind of rifle or shotgun for more than 25 years and had been a member of a junior rifle target/hunter-safety club. First year with a .22 pistol (SW41) I shot about 10k rounds in practice at either 25 or 50 m. (not to mention lots of shooting with an air pistol and free pistol)...
Don't really know what to say about your staining - if you use a copper solvent type cleaner (I've usually used Sweets 7.62) with ammonia: 1.. Run a wet patch through the bore (any gun cleaning solvent - Hoppes 9, Butch's Bore Shine, for example). 2. Soak a brush with the same solvent and run it through the bore a few times. Let it sit for a few minutes. 3. Run a wet patch through and remove it at the muzzle. THEN: 4. wet a patch with the copper solvent.. 5. push it through from breech to muzzle and take the patch off the cleaning rod - pull the rod out. (When you're doing this, avoid getting the solvent on the rifle's bedding or stock.) 6. Wait 10 minutes. 7. Run a dry patch through - breech to muzzle - and take it off the rod. If the patch is stained blue, it's copper deposits. If it's stained some other way, not sure but if it's brown, probably rust. 8. Go back to the original solvent (without ammonia) and run it back and forth through the bore, and keep doing that until a dry patch comes out clean. 9. Run a patch with some kind of gun oil through. Store the rifle muzzle down so any oil doesn't drain back into the action/stock/bedding. 10. Before you go shooting again, run a dry patch through and take it off at the muzzle end. That was what we did at fullbore back when I was still shooting regularly.
And...sorry - spelling 'nazi' here - it's "fouling" I believe "fowling" is using a hawk or falcon to hunt other birds.