I was actually thinking about this the other day when considering the refinish I have to do on an old stock. I have air guns going back to the late 1920's and NONE are finished on the inside of the stock. However, I have had a bunch of rimfire and centerfires that were. And, when you are looking at directions for building stocks for firearms, they usually tell you to seal the barrel channel. As Tim pointed out, any bare wood invites moisture and causes the wood to move. Everyone thinks that vibrations, alone, cause the forearm screws to loosen in springers, but I wonder if it isn't also caused by changes in the wood's moisture content? Think furniture drying out in low humidity.
