I have either the actual chamber casts or proper mechanical drawings -- blueprints of chamber casts of my double rifles.
That and I've saved the roundball bore slugs from each of them, both right and left barrels.

I also have X-rays of the barrels of my double rifles.

If something were to alladusudden go funky with the regulation/load for any of them, I think the first thing I'd do after taking a peek at the crowns is take a chamber cast and compare it to what I got out of the rifle when I first got it. I could also do another pass with slugging the bores, that could tell if there's been erosion or some other kind of change in the bore/groove dims

Funky rib issues... hmmm.
that'd likely come up on an X-ray, compare to original snapshot of the gun and go from there

Wood fit can also lead to trouble, a good hard look at how the wood's doing through the wrist, are there new gaps where there weren't in the past, cracks showing or growing...?

--Tinker