Thank you. I've sent a photo to S&W. It was your comment in post #9 that lead to my backpedaling in post #14 on the "lip." A staking ring seems the best explanation, but post #13 left me wondering (by the way, the cylinder does not exhibit fore/aft play).

Numrich still catalogs the hammer nose bushing for the 12-3, but whether a taller one is available I can't say.