The following two videos come courtesy of The Replica Prop Forum. The host, uh, Star Wars Chick, visits the armory at Independent Studio Services. ISS is one of the major prop rental and fabrication in the Los Angeles area, and they have an especially large collection of weapons, as you can see in the videos below. Larry Zanoff, one of the armorers in the weapons department at ISS, does a great job explaining the difference between real guns and movie guns, the kind of training an armorer needs, and what kind of safety procedures they implement on set.
In part two of the video, Star fires a number of the weapons in their warehouse. I think it is important to note that while movies use real guns altered to fire blank rounds, theatres typically use block-barreled guns which were never meant to fire real ammunition.