My two cents, clearly, but this seems like it is one of the defining bits of the Gunslinger Class. The +1 is nice, but the +DEX mod damage is the real gravy here.
Any guy with a bow, at first level, can add STR damage via Composite Bow. (I won't get into the obvious debate over why Composite Bows should be exotic...) You would think that, at first level, a gunslinger, who makes his trade around this particular piece of hardware, a specialist in firearm combat, should really have that same advantage right off the bat, no?
There are a number of other things to consider, but this one strikes me as a bit silly right off the bat. If not 1st level, perhaps 2nd? I can't foresee why you'd need to wait till 5th level in order to become better than other folk at shooting your specialist tool of the trade.