No, firearms do not typically cost END to use. Any power with Charges uses up Charges instead of costing END (except in some very unusual circumstances).
One caveat: in the full rules (which you aren't using, since CC uses a slimmed-down, "easier to learn and use" version of the HERO System), as noted on page 131 of the second volume of the 6th Edition rulebook, any action costs a minimum of 1 END. So a GM who was being a real stickler for the rules would make your character pay 1 END for using his gun. However, in 40 years of playing this game I can't recall a single instance of any GM using that rule.
