Definitely time for a ball puller, or a visit with a gunsmith.
The penetrating oil might help get the lead out, but it will cause the dowels to swell.
I had always had good luck with sections of
quality oak dowels (not the Chinese hardware store crap). Then, there was an incident that required extreme measures....
The slug got stuck behind a constriction in the barrel. When I whacked the dowel a little harder, it splintered in the barrel and wedged the other dowel sections in place. After very painstakingly drilling (by hand), cutting, and pulling pieces of the dowels out... the slug was still stuck. (The hammer drill was only used for its 'hammer' feature. It wasn't used to drill. And the drill rod had its tip very carefully dressed to prevent any damage.)
I don't recommend using a power tool in any way. I just wanted to show you that you're not the first person that has had that method fail.
For a long time, I thought the "don't use wood" crowd was just a bunch of Chicken Littles that were using cheap dowels. I was very wrong.
Now, I don't use anything but polished O-1 drill rod. That's exactly what you see chucked in the hammer drill, in the photo. That piece of drill rod was 0.003" under bore diameter, and fit quite nicely (bore: .304" / rod .301"). Of course... I only knew that because I had successfully slugged this barrel in the past. If you don't know your actual bore diameter, it's best to get something a bit smaller; so you can put a few wraps of electrical tape on the drill rod to make up the difference and keep it centered.