Spell damage calculation?

I'm a little confused with how spell damage is calculated. I'm refering to non-armor ingoring damage, such as that from fireball.

As I understand it, the damage shown in the spell description is "raw damage", which is the damage the spell will do with no other factors involved. So against a monster with no natural resistance or weakness to fire, and with 0 armor against fire damage, if the spell reads "...deals 120 fire damage" this monster would take 120 damage, correct?

Which would explain why I do ~40 damage against heavily armored units like enchanted warriors with my ele using fire spells.

So, why then when on my 55 necro with 15 AL, when fighting a Hydra if I get KD'd while casting PS so it gets interrupted and I catch a fireball, I take 330+ damage? I really don't think Hydras have like 25+ in fire magic...

I believe the damage is what it does againt a 60 armor target with no deffence againt ele etc, try using foreball on a 60 armor target outside Great Temple Of Balthazar

Hydras are level 22, which affects caster BaseDR: http://gw.gamewikis.org/wiki/Damage

60 AL is the "zero point" for armor portection. Anything below that will increase damage and vice versa. The reason why hydra fireball did more damage is because you were using 15 AL armors which increases the "raw" damage by 118.1% and also hydras are higher level than you but I don't know how level benefits are calculated in GW.