Shooter's Choice bore cleaner says it's for lead and copper fouling, but they also make products that are specific to lead (or copper).
A tight-fitting (new) bronze bore brush of the correct caliber is a must. I'd get at least a 3-pac of those from Brownell's, but they are easy to find at your local gun show. Following Shooter's Choice instructions, I think you will be pleased at the improvement. I don't doubt that there are other makers of excellent de-leading cleaners.