That's a very good question, sir, and one that I've given some thought from time to time. In fact, years ago I turned an aluminum mandrel on the lathe that slides snugly down the barrel. I made up some thin-walled aluminum inserts for the cylinder, and slid the mandrel down into the cylinder during full (cocked) lock-up. All of my S&Ws exhibited near-perfect alignment, but being a novice, I'm not sure of the tolerance, or even if there's one published somewhere. I figured the forcing cone corrects some misalignment to some degree, but I don't know what that degree is. Suffice it to say that if you're shooting clover leafs at 15 yards I personally wouldn't mess.
Seems that every time I comb the used gun racks for a beater that I can learn from, I wind up finding a LNIB safe queen for just a few dollars more and buy it, so I'm not sure if I'll ever learn firsthand about tuning up a revolver. I'd love to hear somebody chime in with regard to checking and measuring end-play and timing.