I've been amazed at how much lead can be inside the barrel of my SR22. I started out its life with a box of Remington thunderbolts, unplated lead bullets. About 200-300 rounds into that session, I started seeing BIG accuracy problems. Took the gun home to clean, and couldn't get the cleaning rod through the bore. Looked down the barrel, and I'd swear it was up to half the diameter in places was obstructed by lead smeared on the walls. Cleaned it as best I could with a brass brush and some oil, but still the barrel looked all scuffed, and not mirror-like shiny as it was when it was new. I was worried I had ruined the barrel.
A friend from work recommended Hoppe's No. 9 cleaner. Got a real small bottle of that, and in minutes, I had my shiny barrel back again. I think I pulled almost an entire bullet worth of lead out of that barrel. I haven't heard about what effect Hoppe's may have on bluing, but I have heard you don't want to get this stuff on any of the plastic parts - it dissolves them quick. But for getting lead out of the barrel, it worked wonders.
I've heard others report that the SR22 only likes plated bullets, and I believe it. I've switched over to Winchester copper plated, and have not had one problem since. I still use the Hoppe's to clean the barrel, but it takes just one wipe with a damp patch, and no scrubbing or soaking.
I highly recommend plated bullets. They're not really substantially more expensive.