The first thing that came to mind, look for a local welding shop and see if they'll sell a single filler wire for tig welding, .125" diameter steel. It'll be copper coated.
Deburr the end of the rod and roll some masking tape around it at the end to not mar the rifling.
Slide it in from both ends and mark the rod so you can measure and see if the blockage is 3 pellets or 15.

Using the rod to pound them out may compact them into a lead block.
I'm thinking of a ball puller for muzzleloading, a drywall screw (head removed) tig welded to the filler wire.
screw it into one pellet at a time and pull them out?

Sorry, that's all I've got.

"Camping places fix themselves in your mind as if you had spent long periods of your life in them.
You will remember a curve of your wagon track in the grass of the plain like the features of a friend."
Isak Dinesen