I don't normally do this, but...Are there any visible examples of the kind of thing you mention? Using your example, I suppose it is also possible that a rust pit the size of a pin prick might turn in to an unseen grand canyon inside the barrel walls. That would be impossible to see unless you were trying to xray all of your barrels, and even then you might not be able to see it. It is the sort of post I would expect to read on Shotgun World.
Your opinion leads me to think that perhaps a slingshot would be my best bet, as even modern guns have catastrophic failures. At any rate, allowing for the fear of termite tunnel rust pits should remove any and all vintage guns from your consideration.
