You said you used Winchester from Wally World, so I'm going to assume it was FMJ. If it was plain lead, that could be the problem. Lead could also be a problem if the previous owner used unjacketed ammo.
There are companies that make stuff to de-lead your barrel. It looks like a sheet of cloth and comes in a package. You cut it into patches that fit your barrel and use it the way you would a dry patch when cleaning. It's a very fine grit abrasive cloth. If you have some fouling in the barrel, that might take care of it.
"An armed society is a polite society." — Robert A. Heinlein
"After a shooting spree, they always want to take the guns away from the people who didn't do it. I sure as hell wouldn't want to live in a society where the only people allowed guns are the police and the military."
— William S. Burroughs