.177 cal?
Get a 1/8 inch bronze Brazing rod from someone that welds, or a welding supply place.
Put the end on something smooth and solid, like your brothers forehead, a smooth rock, or a chunk of metal of some sort, and tap it flat with a hammer. File it to shape to use it as a drill (Google "Spade Drill"). You want it to come out looking pretty much like
http://www.grainger.com/Grainger/MICRO-100-Solid-Spade-Drill-Bit-16R809?Pid=search on the end, but with the last bit a small amount wider than the shank of the rod.
Hammering the end flat saves file work, and hardens the bronze a bit, though not enough to cut steel with. Some careful file work will shape the end. It does not need to be perfect, just pretty close.
Watch that the cutting edge you make, is facing the right direction for the drill to turn. It'll cut faster that way!
Use a electric drill to turn it. A wrap of tape around the rod will prevent damage to the bore if you are worried about the bronze rubbing. One layer of tape only, or the shaft gets too big.
Pick an end, and start drilling. Remove the drill often and shake out the dust, repeat until through.
Drills like this can be used to remove stuck bullets too. Use the largest size rod you can fit in the bore with a layer of tape on it.
Cheers
Trev