Well, actually, there's no spell that connects to ranged attacks to make them use ammo. Instead, they use this
SPELL_ATTR0_REQ_AMMO = 0x00000002, // 1 on next ranged
Put a 2 in the 4th column (In the column number 4 considering there's a number 0 column) of your spell and it should cost ammo.
About "Shield of Righteousness", i've been looking at Spell.dbc and, if u look properly u will see right behind the flat damage of the spell (80th column), a number, in this case, 99. I haven't tried nothing right now, but seems it defines how much of your block value adds into the flat damage. To test it properly, you should swap 99 to 999 to add 1000% of your block value to the damage, if it works, you got it.
PD: Sorry for my english