I clean the barrel and the next 8-10 shot are quite accurate, then pattern gets spread out, pushing a slug thru then measure shows .1775-.1780 . I'm thinking the ammo is not being spun by the rifling and being shaved causing too much lead left behind, does this make since ? I've already replaced the barrel and unfortunately it is same size as original beeman barrel. Oversized bore with almost no choke. Have not found any pellets or slugs with larger dia to try.