[Magic] Missile Spells and NMZ Rules Clarification

[Expy]

I've heard it mentioned that Missile Spells that produce physical effects are unaffected when thrown into or through No Mana Zones (NMZ). While I would appreciate a link to where this is clarified (including what differentiates physical missile spells from non-physical, as I did not see either on the FAQ), my real question is thus:

'If a mage carries a ready 'Physical' Missile Spell into a NMZ or is caught in a Drain Mana -like effect while holding a ready missile, is the ready missile affected?'

At the table it was ruled that -- since dropping the missile in question (Explosive Fireball) would cause it to explode regardless of whether it was then in a NMZ or not (an anaolgy of a well with a NMZ at the bottom was made) -- that physical missile spells were 'tied off' and unaffected by any further changes in ambient mana from the point of casting (rolling of the dice) onwards.

Was this on-the-spot ruling correct, rules as written? Any page or FAQ references you could make would be appreciated and I apologize if I have posted this in the wrong place.

Thanks, Expy.

[Nereidalbel]

Missile spells are physical entities once cast, and fly through an NMZ just fine. However, I'd use throwing rules for launching one inside of an NMZ, as there's a lack of magic to give it initial propulsion.