North: Are you familiar with the Hanned Line Small Game Bullet tool for 22 rimfire? It is a cylindrical tool bored out to accept a 22 rimfire cartridge. The face is hardened and a small portion of the bullet tip sticks above the hardened face. A few licks with a file and voila - any rimfire round accurate in your rifle has a flat nose meplat. That system is not only faster to use than what your doing in a lathe but it also is more accurate in that a more precise amount of lead is removed from the bullet tip. You all ready have a lathe and if you do not have a furnace to harden the tool I am sure any machinist can help you out.
Regarding turning cannalures in bullets I would be cautious. There have been documented cases of bullets separating at the cannelure during target penetration. Granted the impact velocities were higher than what your operating at and bullet diameter smaller. I use a Lee Factory Crimp die for my 356 Winchester.
Check out Norma Alaska bullets and Kodiak Bonded Bullets.
Bob: No I haven't seen the tool you mention but can picture the concept. I could likely make something like that. We have a forge and I make knives so hardening is not a problem. Might give it a whirl if I can find the time.
The Corbin cannelure tool presses in the groove and doesn't cut it in. Perfectly safe. I also use a Lee Factory crimp die but find a double cannelure actually helps lock the core to the jacket when penetrating heavy game.
