What's the earliest you've developed a carbon ring?

I have a 300 Norma that I had chambered by a very well respected smith. The rifle has approximately 25 rounds of factory Norma ammo loaded with 230 gr bergers. Late last deer season I shot a nice 8 point late one evening and left a loaded round in my chamber when I put my rifle back in the safe...dumb I know. I remember the bolt lift was VERY stiff so I took a pic of the brass (included below). A few days later I went to eject the round and the bullet stuck in the chamber while the casing ejected and flung gun powder across the garage. I tapped the bullet out very lightly (pic below) and the bullet had what looked like some corrosion on it. I did not own a borescope at the time so I cleaned my rifle well and put it away for the summer. A few days ago I remembered this whole debacle while I was putting something away in the safe so I grabbed my Norma, put a round in it, and the bolt felt hard to close. Could all of this be from a carbon ring, or are my problems a bit more serious? I have ordered a Teslong bore scope and it should be here in a few days, just thought I would start this thread and see if I may have something more serious on my hands.

ETA: got the borescope in and checked things out. Not as bad as I expected at all, and got it mostly clean. I’ll see how it shoots in a week or so.