Thinking about bbl setback to cure excessive Air Gap, or determining if this has been done previously on for sale revolver. First How is bbl altered to go deeper into the frame? Is the frame and yoke shaved to allow the bbl to rotate one more time on the threads? Or is the bbl flange machined the required amount to allow same? Or can the bbl stud at forcing cone area be stretched in some way to gain length with out shaving the frame and yoke, or setting back the bbl flange? Then, is it necessary to shorten the center pin and extractor rod to accommodate the shorter dimension to the Locking Bolt? Revolvers in question are one pre mod 27 looking tight in the end of extractor rod to locking bolt relationship with pin sticking forward from locking bolt recess groove while cylinder is closed. One other revolver is 29-3 in proper time and no endshake showing more than .010 air gap. Is there a possibility in twisting or damaging the frame on non pinned 29-3 revolver thru removing and replacing said bbls?

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It is my understanding that the CORRECT way to do this is to relieve the barrel rear face rather than shave the frame. You pretty much ALWAYS remove metal from the cheaper, more easy to replace part. I have seen a Colt New Service that had the front of the frame relieved, badly, and ended up with the barrel pointing down noticably. There is always the possibility of tweaking the frame, but if you have a competent man with a good frame wrench it isn't at all likely. If you only have one or two turns it isn't usually a problem for the extractor rod. It isn't that hard to shorten an extractor rod if necessary. I had this done with a 625 that was spitting badly and had an obvious angle on the forcing cone. After the work it shoots beautifully and wasn't terribly expensive.

Yes, it's usually necessary to shorten the center pin and extractor rod. Setting the barrel back one turn moves the barrel 0.0277 in rearward.

Not sure what you're describing, but if you can see the center pin sticking out beyond the end of the extractor when the cylinder is closed, something is wrong.

If the proper tools aren't used, it's always possible to damage a frame while removing/installing barrel. Contrary to myth, there's no difference in torque on the barrels between pinned/non pinned barrels. Any threaded fit is managed by tension between the bolt head/nut/barrel shoulder and the threads. In extreme industrial applications, the threaded stud is stretched by a hydraulic jack and the nuts are spun down by hand.