Okay. A player of mine chose to take the spell from TSS#9 called Cake Ammunition:

Cake Ammunition (Elemental Manipulation)
Type: P · Range: LOS · Target: Obj Res Table · Duration: I · Drain: +1(S)
This spell uses the elemental effect of blast to ignite all ammunition in the area of effect. This is a very dangerous spell, as it can cause very big explosions if the spell is successful. To determine if the spell is successful, the Object Resistance Table value of the strongest ammunition in the area of effect is used as a target number to ground the spell. (Restricted Target: Ammo)
(emphasis mine)

It's somewhat a moot point for the moment because that same character is also behind bars awaiting trial for around a dozen counts of assault with an illegal spell after having used Cake Ammunition and gotten caught.

In the interests of time, I allowed him to use the spell last night, I think with a TN of 6, just picking a number that wouldn't be too hard, but also not too easy. However, in case he or others pick the spell again, where can I find Object Resistence values for ammunition? I looked around in SR3 today but couldn't find any information about it.

-- Dash --

Probably 5 or 8, since that covers most processed (but not highly processed) materials. Really high tech ammo might be a 10 or better.

SR3, p182 for the OR table. To determine the effect, you roll 2d6 and add a modifier based on the damage level of the spell. Since it's doing S drain, I have to assume it's doing an M strength effect, or +4 to the OR on the test... All in all, it looks like the spell isn't designed in line with MitS (which is quite possible).

[edit]The problem with the spell is that it wants to be an elemental manipulation so that it can affect unseen ammunition while keeping the benefits of being a transform manipulation (ie, making ammo directly explode). Elemental manipulations summon indescriminate energy which isn't generally very sophistocated. Essentially, you might end up with a spell which does this as a secondary effect, but not well (ie, requiring a 2d6 roll vs. OR modified by level, and the primary effect is wasted) or a spell which does it as a primary effect but can't target unseen ammunition (a transform manipulation). [/edit]