When you have the cylinder open check the that the end of the bolt is flush with the face of the breech face. If it is, that is exactly where it should be. If it is below flush it is most likely there is debris inside the action causing this, open the gun up and clean it. If it ever was correct there is no way it could ever get out of adjustment!
Second thing to check is the front end of the extractor rod. This assumes you have already verified the extractor rod is tight. Remove the cylinder from the gun. Place it, extractor down on a hard, flat surface. Push down so the center pin is pushed flush with the center bearing of the extractor, the front end of the center pin should be at least flush with the end of the extractor rod, preferably just slightly above. Check by running your finger over the end of the extractor rod. If you can tell you are running over a hole instead of a flat surface, or you can catch your fingernail inside the extractor rod, it needs to be shortened until you do not notice this.
The extractor rod can be shortened with a fine file (If you can file flat/square. This isn't as easy as it sounds!), a lathe, or chuck the extractor rod in a drill press and either use abrasive paper or a fine cut file laid on the drill press table to shorten the extractor rod. This usually is only a few thousandths, even if this is a new extractor rod which has never been properly fitted.
Extractor rods are one of the most frequently replaced parts in a S&W revolver. The reason is there are so many "Bubbas" out there that think the knurling is there to grip with a pair of pliers to tighten the extractor rod. It takes once and the knurling is destroyed and looks like s***. The next owner buys a replacement and just sticks it in the gun without fitting. He finds he has a gun that has problems opening, doesn't know why, and sells it so it will be someone else's problem. You already know the "rest of the story".
