1. Have to admit I've never been there personally. I've heard people, real people, who have no reason to disinform, complain about the problem, and other people, who witnessed it, confirm the cases. The cases involve tightly choked guns, slugs fired without checking out if they fit the chokes, and the loss of efficiency happened with a very limited number of shells fired, resulting in both density and evenness loss. The hunter would finish the bird season with the gun and everything's fine, then take the gun for its first big-game season, and everything's fine too, than come the next bird season and the hunter realizes he can't hit anything with the gun at long ranges any more. Might be something psychological, might be an old wives tale, wouldn't bet my bottom dollar on that, but the folks who taught me shotgunning warned me about this potential problem, and I'm passing the warning. Edit: the warning didn't imply that every choke will be damaged by any slug, just that it can happen if one is doesn't know what one is doing.
2. Not to my knowledge.
3. Me too, but the cases of barrells coming apart from firing slugs that I know of happened to the brands of guns that are notorious about ribs coming apart with anything harder than regular hunting use, so I'm not sure whether the culprit is shooting lots of shells or shooting lots of slugs.
4. Erm, yes, sort of. I loaded once a few of "old-timer" loads with a ball that would come through the full choke of my Izh54, paper hulls, felt&cardboard wads and black powder - it's a bother to get a 17.5 mm ball center in 20 mm hull, btw - but I didn't get to test-fire them for accuracy, and they ended up wasted during a plinking outing by my wife, busting up some outdated computer equipment
So they worked, but I have no idea how well
