Mage & Firearms Damage

Some of my players and, frankly, me, are not quite understanding how it works. The book says that when you become adept at a certain thing, you can get an automatic success. When you're using firearms, like a .38 special (6-round revolver) how does that work? How is damage done? The firearms table in the book gives the damage, but it doesn't make sense. Is the damage per bullet or for the entire clip. If its for the entire clip, then how much damage does a single bullet do. Sorry if this isn't clear and if it isn't, please let me know. I really need some help with this guys, so please respond. Thank you.