I'm not a regular here, so please forgive if this has come up elsewhere, but if so I haven't found it.
In tonight's game my character found himself on the receiving end of a foe wielding a wand of magic missile. A pit prevented me from closing to melee, so it's a ranged duel of martial vs (item) magic. Figuring that getting hit while casting is generally worse for the other guy than getting hit while not casting, I ready my action to shoot him with my crossbow the next time he speaks. The enemy then uses the wand (thus triggering my readied attack).
While luck wasn't with me this time (Natural 1), the question remains... If I'd hit/dealt damage, what happens? Nothing further? Or does he have to make a concentration check to avoid having his action disrupted?
I know spell trigger doesn't provoke attacks of opportunity (the usual source of spell interrupting damage).
I know the Concentration section says "In general, if an action wouldn't normally provoke an attack of opportunity, you need not make a Concentration check to avoid being distracted." Two things about that stand out to me, "In general" strongly implies exceptions, and "to avoid being distracted" in this context seems to imply a deliberate choice to make the concentration check (i.e. casting/skill use defensively or against an environmental distraction). I don't get the impression that it is meant for taking surprise damage from a readied action.
I see #2 on the table: 10 + damage dealt "Such as during the casting of a spell with a casting time of 1 round or more, or the execution of an activity that takes more than a single full-round action (such as Disable Device). Also, damage stemming from an attack of opportunity or readied attack made in response to the spell being cast (for spells with a casting time of 1 standard action) or the action being taken (for activities requiring no more than a full-round action)."
Whatever the components or relative effort required, the magic missile is certainly a spell taking effect, so it presumably counts as "being cast" when the trigger is said. So, can that "casting" be interrupted by a well-timed crossbow bolt to the chest? I realize logic and verisimilitude aren't always the most reliable guides in rules interpretation, but I can't help but imagine the poor wand holder getting the first syllable out and then... "AvaURGH!" nothing happens. Am I right?