Well, I'm not a professional gunsmith by any means but from what I've learned over the years, it boils down to what you're going to be using your guns for. If you're shooting strictly jacketed bullets, you can go with tighter end shake and barrel/cylinder gap, say a couple of thousants on end shake and 3-4 on b/c gap. Depends on your powder also, as a clean burning powder will do better with the tighter settings. But if you want a study diet of lead bullets, it needs to be a little looser, particularly on B/C gap, due to typical lead buildup, maybe up to 6 thousants there. If you're into black powder, particularly the real stuff, not substitutes, then a lot looser, maybe 5-6 on end shake and up to 10 on b/c gap. As far as measuring it, force the cylinder back towards the recoil plate as far as it will go, stick a feeler guage that just goes in, between the gas ring and cylinder frame and that's the end shake measurement. Then, put another feeler gauge between the cylinder and barrel that just fits and that should be the b/c gap. Hopefully some real gunsmiths will chime here if I'm too far off.