The smooth shank end off a drill bit works. Slide the end of the bit in past the divot, and gently apply pressure to move the divot back into place, either by tapping opposite the divot with a punch and hammer, or by applying force by prying, all while watching the results closely.
You may need to jury rig a means of applying force in the correct direction, depending on the location of the firing pin.
It would be pretty easy if you had a drill index with a full set of number and letter drills, but I would suggest somewhere around a Number 2 or 3 is going to be a pretty good fit into the chamber.
Another option, is simply to make a chamber iron tool. For a one time use, I would not even bother to harden it, but hardening it is easy enough. Gun barrel steel is soft, in the scheme of things.
Start by making the end of a piece of music wire (Model Airplane Hobby Shop, used for landing gear, among other things) the correct diameter, either in a lathe, or with files and sandpaper while it is spun by a drill or similar methods.
Polish it smooth and to size with around 320 or so wet or dry paper, wet.
File a flat down one side, about a quarter of the way through., this will make the end a "D" shape.
Fix the rod to the work bench or have another person hold it steady, and take a strip of the same sandpaper and whipsaw it across the flat to round and smooth off the corners of the "D"
And that's pretty much it.
If you want to harden it, heat the end red hot and plunge it into a glass of cold water. A smear of soap (heavy smear) will help reduce the scale and crust that will form.
Polish the hard rod end with wet sandpaper, then apply heat a few inches up the shank and watch the color travel up the bar. when you see the first bit of color reach the mid section of your iron tool, back into cold water to stop the tempering. This will leave the end pretty hard, the shank softer, less prone to snap if pried sideways.
Takes less time to do than to tell about.
Other possible tools. Look at any screwdrivers you may have. Round shank, good enough steel, good handle... Use you brain. If you go in there like King Kong digging for a booger, you can pretty much expect the job to look like one when done, eh?
Cheers
Trev
