a good way to look for blatant disrepair, since as diyj pointed out typical wear isn' t usually noticeable, just putting a bore light down it and checking it out with your eye works, but instead of looking straight down the bore, use a steady hand and you can focus on individual parts of the bore, I usually cant it outward and start looking at the throat on one side, work straight up, and do that for 2-5times all the way up around the bore. Doing this I can see almost ANY rust in a bore, and any problematic deviations such as pitting and fouling, checking actual groove integrity is pretty much best left to a bore scope though.