I guess I'll poke my head in. @~Rayleigh is really wrong with his sarcastic statement. Guns have zero magic attack. So the damage will drop drastically. However, there is a minor work around. Around the time Nightmare was added, Rangers gained the ability to use daggers. On the surface, that is pretty useless. Though it is a decent compromise as you can equip a dagger with a 1h gun to at least have enough magic attack to deal damage with the skills. It won't be as strong, but it'll be usable. So if you want to keep the full power of the Elfeen skills, you have to keep the bow. If you want use the skills with one hand guns, you have to equip a dagger. 2h gun won't work unless you have an insane amount of strength (which isn't recommended at all). Even then, it wouldn't compare to the other versions I mentioned earlier.