Plenty with Google search.
Remember CF & RF are often different because RF is really carbon/lead in the throat and CF, right at end of chamber.
CF vintage guns often don’t show much, most if not all RF’s especially rarely/never cleaned ones do usually discovered when chambering gets tough.

Joe a real good indicator is when a rifle just stop shooting. 
Several years ago Duane Jenner went to out practice for a match coming up here on the coming weekend. 
Wednesday the rifle and a 25 Hornet was shooting just fine. Thursday  morning he went back out and the accuracy completely fell off.
He brought it right over for us Barry Darr and myself to look at and did have a Carbon ring that if looking real close could be seen.
I brought out a cleaning rod, a wrapped Jag and the JB and it took me over an hour and none stop to finally get it all out. 
He took it back out on Friday morning and the day before the match and the previous accuracy was now back. 

Interesting. After looking at examples in Google images, think I may have a rifle with carbon in it. My old Sportco 308. I always thought the cracks were in the steel itself.