You're right, damage charms are specific to melee weapons; I never really paid attention to the description before (aside from the relatively low damage amount), and didn't use any charms.
I've put a normal damage enchantment on pretty much every bow I've used with an enchantment slot, though, and it does increase the ranged damage.
..

.. Raze
I went back and checked and I did have it wrong so now my two dual wielded weapons
have a
519 - 602 combined damage. I also enchanted the Scorpion two hander
with normal, magic and level 9 fire and it now replaces my old one.
Divine Melee Damage charms add a +10 to melee damage. I just got one but am not using
it as there has to be better weapons available.
The enemy ..

.. don't stand a chance against the good guys ..

.. .
....

.... .
Kel******