[ithacaartist]

If the nub is worn down, run--don't walk--to a professional welder who is virtuoso with the TIG. This process will be most precise (except, perhaps, for micro-welding) in depositing as much or as little material where it is desired, and it will be more durable than a foreign substance such as J B Weld.

The sprung ball method, ala Erma, would be most elegant. Use a machinist with an EDM machine to create the hole with no worries about temper or finish of the piece. The early, mostly Zamak Erma .22s use a 3mm ball bearing and an appropriately-sized spring. I have not seen any that were actually staked, however, which I'd not recommend on a cast Zamak part, anyway. It is basically retained by the minimal gap between the back end of the lever and the side of the ear of the frame. If the hole and the lever's shaft are considerably worn, sometimes enough play is present for the lever to tilt up and away from the frame, which allow the ball to escape. You can tell the ones on G.B. that have lost their balls--the end of the spring makes messy gouges in the finish if the gun is not repaired immediately.