You're supposed to clean them??
I just choot'em.
Seriously though, I spoke to Woody from LW at SHOT one year and he said using Sweets and some of these other harsh copper remover/chemicals do more harm than good. He told me a story about a new barrel that went out and came back from a guy using a "break-in" process, who used one of these chemicals, and it ruined the barrel. I wish I could remember which specific one it was (I may have the interview footage still on a hard drive).
Anyhow, I bought one of his barrels after that talk, and didn't do a "break-in". And guess what, it's still the most precise AR-15 barrel I've ever owned (followed closely by a 20" Stealth barrel).
So, my break-in is just shoot the thing. I don't clean my barrels until I see a degrade in performance.
Just my $.02, which I'm sure many will disagree with.