Shim is 303 SS.Bump
Drops onto the rear of the cylinder with 2-3 thou clearance, and does not interfere with the hand.
OD was a bit of a compromise ... I wanted the outer diameter to be at least as large as the ring on the frame, but this would have caught the hammer when it closed. So had to reduce it slightly to clear the hammer. As it stands, it sticks out into the cap pockets a bit but not quite enough to prevent access to the caps. Nipples are the longer ones from Track of the Wolf to make up the extra distance caused by the shim.