The main problem is that once you shoot a target, it closes range and you can't shoot again. Or if you find a guy that will attack from a distance, we will kill that target in a minute or 2. But there is hope! Blizzard has given us a target who's sole purpose seems to be for leveling up ranged weapons (ignore the quest he's involved in).
In Netherstorm there is an NPC named "Dr. Boom", you can find his location here:
This NPC has 350k health (or so) and does not move. Nor does he do any ranged attacks that he can hit you with. So, you can sit back with your favorite ranged weapon and shoot/throw away at him.
Enjoy!
