IronMonkey,
I have been shooting my Super 14 in 30-30 Winchester caliber with cast bullets the past couple of days (the weather got above 20 degrees!) and I also have some leading. It is not in the throat area though. My rifling gets gray colored toward the end of the barrel. It is somewhat difficult to remove also. I use J&B Bore cleaner and Butch’s Bore Shine mixed into a slurry. I suspect any bore solvent would work with the J&B. And, I do use a stainless steel brush…Yea, I know about a hundred people are going to say I am ruining the bore, but I haven’t ruined a bore in dozens of years using the steel brushes!!!
My opinion is that the Contender barrels are extremely rough when the come from the factory. Tool chatter is always visible using a good bore light. Considerable shooting/cleaning are necessary to smooth the bore and help prevent fouling—be it lead or copper fouling. My particular 30-30 barrel will shoot at least 30 rounds before I notice any accuracy problems. And then I am not sure that it is effecting accuracy at all. I have yet to have a Contender barrel that is a tack driver with cast bullets. Don’t know why but that is the case. All the barrels I have will shoot jacketed bullets very accurately.
I do seat my bullets to just touch the rifling. I am shooting the Lyman 311041 and the Lee C309-150F bullets cast from an alloy of 2-1 (ww-#2) and they are then heat treated to a hefty BHN. The hardness varies, but it is always in the mid-20’s. Liquid Alox is used as the lube. I size only the check when seating it to 0.310”—the rest of the bullet is “as cast”. I sure wish I could get my Contender barrels to shoot cast bullets as well as they shoot jacketed bullets!!! Good-luck…BCB