I think it's time for a reality check. As they say "knowledge is power" so I'm going to whip some knowledge on you and make you more powerful. All Ruger firearms come with this silly paper thing called an "Owner's Manual" .... most people don't read them but they do contain some valuable information. Let's start with "dry firing". The index in the funny GP100 manual says dry firing is covered on page 12. On page 12 in big letters it clearly says DRY-FIRING followed by a short paragraph:
"Dry Firing is practicing the trigger pull of the empty revolver for practice and familiarity. The GP100 revolver can be dry fired without damage to the firing pin or internal components."
It just doesn't get much clearer than that! Just below that paragraph is another piece of wisdom. "Do not dry-fire the revolver with the plastic "safety disc" on the cylinder. Again ... RTFM.
It bothers me when people respond to threads when they don't even have the same model gun as what the OP was asking about. I looked at my own KGP-22-55 (GP100 22 LR) and found the extractor was machined just a tad short of mating with the body of the cylinder. It looks exactly like the OPs. This machining creates a very crisp line .... not dents from a firing pin. If you push the extractor rod in just a little, you will see exactly why there is a line. Further, this gun is a "rim fire" which means the firing pin strikes the very top of the rim .... not the center of the chamber where the "line" appears. So .... nothing in this thread has any merit .... meaning the gun is perfectly normal .... just as the Ruger Rep said and there is absolutely no reason to send it back to the mother ship unless there is something else that doesn't work.
Finally, I'd like to comment about "generic" issues like dry firing because it comes up quite often on this forum. ALL RUGER HANDGUNS ARE DESIGNED TO BE DRY FIRED WITHOUT DAMAGE TO THE FIRING PIN OR INTERNAL PARTS. That statement does not apply to other brands of rimfires or even centerfires so you really need to look in the owner's manual for guidance in that specific brand/model. If you are too lazy to read the funny manual, then by all means .... don't dry fire other brands of rimfires.
Just an FYI concerning dry firing any Ruger DA rimfire revolver .... the firing pin is designed for limited forward travel plus the chamber mouths are countersunk. This means when the firing pin is at its maximum forward limit on an empty chamber, it will not touch the chamber mouth .... it just hits air. SA rimfire revolvers are designed the same way. With centerfire SA or DA revolvers, the firing pin is in the center so all it hits is air when dry fired.
I do NOT recommend using Snap-Caps or wall anchors in any Ruger handgun. Why? Because of Ruger's design, they do absolutely NOTHING to prevent firing pin damage, however they do give the owner a false sense of security .... thinking they somehow protect the gun, which they don't. It's kinda like thinking an oil change in your car will give you better traction in snow .... totally unrelated. Spend the money more wisely on ammo or apply it to accessories like a holster or grips.