For really nasty carbon, try kerosene. If you're really anal about it, as I suspect you are, you can use an old Sonicare brush head, modified to fit the chamber. I use mine on some pistol parts and cleaning bolts. It's a nasty, messy process, so do outside and wear proper PPE.I haven't heard too many accounts of chemical soaking action working very well on carbon.
Also beware, kerosene can remove bluing, so only use it on stainless.
I wouldn't even worry about the muzzle pitting. There's a lot more going on on an Axis rifle that would cause the occasional flyer.I'm not too worried about the cross hatches in the Tikka or the drill marks in the savage. So long as they shoot as well as I need then it's all good!!
I just got the borescope because I wanted to learn what is going on in there. I hope to not cause myself any unnecessary stress and anxiety!
I usually go hundreds of rounds between cleanings, when either the chamber mouth looks dirty, or I see gray carbon start to form on the crown.