As Colorado mentioned, it's usually best to create a new thread for each question you have, (after you do a search on it first of course) becuase it can become very confusing, very fast.
That said - In regards to dry-firing various firearms, Colorado nailed it in that most centerfire arms are fine to dry-fire. Rimfires, however, can sometimes be damaged during dry-firing due to their firing pins having the tendency to impact the chamber face when the trigger is pulled.
As with all things, read the manual for the particular firearm you're working with at the time for the definitive answer.