At a guess, the gunslinger adept has been tweaked out pretty well (from the archetype) so he has a higher Pistols dice pool. Then put him with a pair of Ruger Thunderbolts and APDS ammo (or EX-EX, if he's a starting character). Then he's throwing out as many as four narrow bursts on his first pass. For APDS ammo, that's base damage 7P, AP -5 for a narrow burst. (For EX-EX, it's 8P, AP -2 for a burst.) Just remember the recoil for those bursts.
Also remember that if he's shooting four times, that's twice with two weapons, and he has to split his dice pool between the weapons (SR4A, 150). Even so, you're probably looking at someone who's splitting a 20-dice pool. And remember DP modifiers come after the split. So, for example, if he's shooting each burst at a different target, that's 4 targets, so he takes the multiple targets modifier (SR4A, 152). That's -2 for the second target, -4 for the third, and -6 for the fourth. Also remember the full ramifications of using two weapons (SR4a, 150): Lose any smartlink or laser sight bonus, and recoil from either weapon affects the other. My guess is that some of these modifiers aren't being applied.
Gunslinger adepts are supposed to be deadly, but they're not reliable for tougher minions or multiple harder targets. If this is a character playing in Missions (which, given the thread location, he is), the GM should be using the Pushing the Envelope section...there's plenty of time left in the time slot if the adept is ending the combat in one IP. If this is a regular game (and you say it is), talk with the GM about it.
All that being said:
If this character really wants to go first, there is a cheaper way than spending 15 BP for Adrenaline Surge. All one really has to do is spend a point of Edge to go first (SR4A, 74). If the gunslinger adept at your table is breaking combats, there's an underlying imbalance that goes beyond the Adrenaline Surge quality.