A word on "chamber ironing".
I wanted this to be seperate.
As many know, rimfires, particularly older ones, will get a burr on the edge of the chamber, which has been beaten there by the firing pin from dry firing.
The metal is not gone, it has been pushed from the breechface into the very leading edge of the chamber.
If the burr is simply removed, by either cutting or filing it away, the low spot in the breechface will remain. This will often cause misfires, as the brass from the shell casing is swaged into the groove, instead of being crushed between the breechface and the impacting firing pin.
Therefore, using files, a drill, a reamer, or a tool that is grooved and rotated in the chamber is not advised.
The metal needs to be pushed back outward, to refill the groove in the breechface. This would necessitate pushing the metal from the chamber opening outward, which is much less likely to happen with rotation. Further, a strictly tapered punch will push out the metal right at the edge will still leave a smaller burred section just inside the chamber opening.
The tool mentioned above that was previously available had a leading tapered section so that it could be started, and then a short straight section that was chamber diameter, with a step to bottom out on the breechface.
Once driven into the chamber until it stopped, the burr would be pushed outward into the groove in the breechface, nearly or fully filling it back in, and the step hitting the breechface ensuring that there was no raised metal on the Chambers edge.
Yes, one can be made with a lathe, my personal one I made myself. It should be made of a hard steel, not mild steel, so it is harder than the barrel.