Re: Scratched the Chamber Shoulder
A surface inclusion in the cartridge chamber area can generally create two types of headaches.
One is it marks up the brass and in the most extreme of cases, it could lead to reduced brass life because you now have a stress riser. I'm splitting hairs and being a bit philosophical here as I've never personally seen this happen. Be that as it may I'm fairly certain that if I take a file or scribe and mark a big deep ring on my brass someplace it's liable to split along that mark if I shoot enough.
Second is it will make extraction either impossible or difficult. this is usually limited to Rings being cut in the chamber during chambering due to poor chip evacuation.
In your case from what your describing I'm inclined to believe that the gun will be just fine if the "woops" is limited to a little nick in the shoulder. If it really bothers you, slather some 320 or 400 grit lapping compound onto a fire formed case and lap any raised nicks/dings/burrs out of the shoulder. Solder a rod into the primer pocket so that you have something to wrestle the case with.
Then wash the snot out of that gun afterwards and USE A BORE GUIDE ALWAYS from now on!!! Can't stress that enough.
More gun barrels are ruined by haphazard/too frequent cleaning sessions than by shooting. I don't clean gun barrels until I see a reduction in performance and it is just for this reason. Every time you stick something in your barrel you run the risk of damaging something. You CAN leave a bore fouled. The ol cardinal rule of a dirty gun is taboo stems from the days of corrosive priming compounds. Those haven't been used for over 60 years.