There's a whole lotta truth in that statement. I got it out of morbid curiosity, and so I could differentiate fouling from decay. No sense scrubbing the rest of the 'fouling' out if it's actually pitting and you take the rifling with it XD. I got a better look and the 'buildup' is just pitting. THe way the light was reflected by the mirror created the illusion of buildup.
Sometimes they have nice surprises too. I scoped my K11 without swabbing out the automatenfett and was greeted by a bore over 100 years old that booked brand new (orange is the grease and some copper in the grooves)
Attachment 117702
I now own a mini lathe that I am slowly getting into shape. trying to fit everything to within a few tenths. After that, I'm going to custom build an expanding mandrel (2 points of concentricity) and a bushing for my 30-degree neway cutter and put a bit of life back in that crown. Dave Manson only offers an 11-degree cutter and there's no way I'm putting a flat target crown on a milsurp. I may also have a 1-hp 8x22" vertical mill en route.