Nix on the "fishing weight".  Those things are made of unknown alloy, including scrap with plenty of scratchy contaminants. Use something intended to be passed through a gun barrel, like buckshot.

And while a wooden dowel is OK for starting the slug the first couple of inches, NEVER attempt to drive a slug all the way through with wood - which can split, splinter, and wedge itself most horribly! Use a smooth solid steel rod with a flat face for pushing the slug through.

---