Why doesn't it work? I, a 17th level Fighter, have a loaded heavy crossbow, which I spent a move action to load (unless I am proficient in martial weapons, in which case it was a free action), and I see my target, a juicy demon that's just finished cutting through some helpless low-level adventurers.
My crossbow is a +5 crossbow, I've got a 17 Dexterity, and weapon focus, and greater weapon focus, and weapon spec, and greater weapon spec, and improved crit (crossbow). I have bonuses of +27/+22/+17/+12 to my attack roll, so I fire my arrow, and make four attack rolls. Two hit, another criticals, one misses. I only fired one arrow, but I'm such a danged good shot, that one arrow does more damage than a less-trained person could manage. With one shot (but four attack rolls), I deal 4d10+16 damage.