psst
It'd be possible to do a weapon with both melee/firing attacks, but it'd be lame. It'd go like some Morrowind/Oblivion mods, in which upon acquiring the weapon, you'd acquire it twice, except one version would be ranged, the other would be melee.
Infact, morrowind/oblivion had it better this way, because you could make it so the weapon had a spell you could use, and when you used the spell, you could switch out the weapon for it's other version, meaning to change from melee to ranged you had to use the spell.