Remove the grips, sideplate, mainspring, mainspring tension screw, and hammer.
The hammer nose striker ("firing pin") is held in place with a hollow rivet.
The easiest way to remove the rivet is to drill it out with a drill slightly larger than the hole. Careful here.... if your drill is too large, it will ruin the hammer for fitting a new rivet. Punch out the old rivet with a pin punch or small nail set. Clean the cavity with solvent and brush.
Replace the striker and spring, and secure with the new rivet. Work the striker to make sure it and the spring moves freely.
Support the hammer and rivet on a solid metal block. Set the new rivet by lightly peening with a rounded punch. Confirm that the nose and spring still moves freely.
