I've used birdshot and BB in percussion revolvers with some success. The trick is finding something that will hold the shot in place. I used card wads ands cork wads, which work well enough at the range, but probably wouldn't hold up if carried in a holster for any distance. Patterns, of course, were awful, and a smooth bore would probably go a long way toward fixing that problem.
I never used them on any critters. Milk jugs and empty soft drink cans reacted to them with maybe a bit more energy than with .22 shotshells, but not as much as with .38 and .44 shotshells. I figure they should serve the same purpose as .22 shotshells, ie. for close range rattlesnakes and such, but I wouldn't count on them for much else.