If the chamber had been lengthened here in the UK it does not have to be reproofed by law.Don't ask me why?
A few years ago it became fashionable to lengthen forcing cones to reduce recoil and enhance patterns.Every gung ho gunsmith bought a Clymer reamer and had at it.
I never bothered, just carried on polishing wood.
Now it seems no-one else bothers?????
Fashion??
I am still waiting for Drapes & Crepes to come back into fashion, unfortunately the quiff went longtime ago.