Re: dry firing
In youth rifle programs, we encourage them to dry fire-- the rifles they are using are usually higher end Anschutz's, FWB's etal. You can dry fire them all day, and should!
It's usually the cheaper .22s that wind up with the problems, because of exactly what has been said already-- it can peen on the rim of the chamber, such that it will eventually cause a buildup of material on the lip. When that happens, you cannot get a shell to completely seat in the chamber, and the chamber surface has to be re-surfaced.
I have a picture of a damaged chamber, but I'm at work right now and our firewall won't let me access photobucket-- go figure. I'll post it later tonight.