Unless people in the radius of the spell are fried to a crisp, I wouldn't. It'd take several hundred degrees C temperatures through a magazine and the cartridge case (or several hundred more degrees C through just the magazine for caseless ammunition) to set off the propellant -- consider what happens to a human when his skin is heated up to a few hundred degrees C.

In the freak occurrence that sudden, open flames would not kill the person in question but would cook off ammunition, it'd be one round at a time, absolutely no chain reaction. If the cartridge happens to be aimed at you, it'd be like a being shot with a very underpowered version of the same cartridge through a weapon (no barrel = very low bullet velocity).

If the bullet doesn't point your way, you might get scratched by fragments of the casing, or even get wounded by the case end (definitely no more than 3L). With caseless ammo, unless you're storing it in your pants pockets, no damage. Armor should count as normal -- most people don't store their ammo inside their body armor.

Of course, if you like cartoon-like, comical games, run it whatever way is most fun.

Yes, it does, but that doesn't mean it makes any god damn sense at all.

Note: according to the rules, an elemental doesn't automatically do Engulf damage to everything in/around it, it has to use the Engulf Exclusive Complex Action for that, or use a melee attack. By canon, then, throwing the minigun and ammo at it wouldn't work

Using common sense, a pillar of flame hot enough to immediately cook of 800 rounds of minigun ammunition (belted and in a drum, I assume) would also be hot enough to ignite everything (paper, plastic, wood, paint) near it, melt plastic floor mats in a meter radius, and most importantly kill (or deal lethal damage to) any human being within less than a second of direct exposure.

Further, from a common sense perspective, the "volatility" of (EX-)Explosive small arms ammunition is horribly exaggerated in the rules -- no ammunition type that causes the weapon to explode in one out of every 216-1296 times it's fired carelessly would ever become a hot commodity. It'd still take several hundred degrees C through 2 insulating layers (the drum and the bullet jacket) to set off the incendiary and then the explosive -- and again this'd have to happen to every cartridge separately, there'd be no chain reaction.

Assuming there is a sudden increase of several hundred degrees C through those 2 layers, (EX-)Explosive ammunition would only be more dangerous if it goes off in contact with you. The detonation of the bullet might add a little bit to the fragmentation of the case that you'd get with any cased bullet type -- but then there'd be no bullet to shoot out, and thus the fragmentation of the cartridge case and the bullet jacket would be the only devices for causing damage. That's well sub-Hold-Out Pistol damage, even if it's in contact with your bare skin, and any armor at all would stop the fragments.

And just think for a moment, how stupid is it that an ammo cook-off happening several meters away from you would somehow magically bypass all your armor, while being shot from that distance wouldn't.

Yup. You can't say you're not an obvious call for situations like that.

While the Flamethrower and Fireball spells on sr3.197 or the Elemental Fire Secondary Effects on mits.52 don't spell out that ammunition catching fire automatically explodes, it seems to me that was obviously the intention. In the part where the GM is instructed to determine the appropriate secondary effects (mits.51), it even says: "For example, a Fireball might start fires, cook off ammo, ignite fuel tanks, and set fire to armor and clothing all over the blast zone." And then there're the specific rules for dealing with ammo cook-off or explosions, included both in the Flamethrower/Fireball description and Elemental Fire Secondary Effects.

True enough, that might leave a GM enough wiggle room to say that ammunition (or grenade, or explosives in general) cooking off is pretty much never an "appropriate secondary effect". But without RL knowledge of how ammunition and explosives work, the rules definitely imply that cook-off is appropriate.

Um.. no, it's pretty much a universally bad spell.

Let's look at an example, shall we?

Assuming that the mage wishing to cast enhanced aim does as you suggest and sinks all of his available dice into casting the spell, for an average mage with no foci or totem modifiers that's what, 12 dice? On average, he'll have two successes. Now, assuming he's a non-initiate with no magic loss, his enhanced aim will work on targets within force * 6 meters. Let's assume he's casting at force 6 (though he'd only need force 2 to take advantage of his two average successes). So, he can target anything within 36 meters. Not super useful for long range weapons, but we'll let that be for the time being. Now, the fun part: Any target in range gets to resist the spell! Plus, it's NET successes that determine the target number reduction! So, if one of our mage's targets happens to get a single success when resisting, that drops our mage's average net successes down to 1. Which is not enough to warrant ANY target number reduction. Plus, in order to avoid having INCREASED target numbers for sustaining the spell, he'd need to have a sustaining foci (or one of the other things mentioned in this thread). A force six sustaining foci is extremely expensive and karma intensive, and counts towards your limit for foci addiction. If we drop the force to avoid paying for the foci, this means that the targets will likely have even MORE successes, plus you'll have a much reduced range.

Of course, initiating can help things, and you can cast the spell before combat to get more than just the average number of successes. However, rolling against sixes is never gonna give you a lot of successes with realistic numbers of dice. So, once again, you're looking at maybe -1 to -2 to TNs BEFORE the target gets to resist. Factoring in the whole "resistance" thing, you're not going to be seeing too much use out of this spell.

No, I read your posts- I was just illustrating how, even with such resources, the spell sucks.

You used a fairly restrictive and biased example to "prove" that it "sucks". PCs get Karma (which alone nearly doubles the amount of dice rolled for the spell). PCs can sustain spells using ritual sorcery (which is 600¥ for a Force 6, a lot less than the typical binder on a run). PCs can bond specific spell foci, use totem/elemental dice, and all sorts of other ways to boost the number of dice they can roll. An "average" PC mage will be able to toss 12 dice at the spell. A specialist will be able to toss 20 to 30 dice at the spell, at least, and then Karmically reroll once or twice to boost their success ratios.

Compared to a smartgun link specifically for the situation of using firearms, it's not as efficient. But it's the only way to reduce TNs for Elemental Manipulations, and one of only two ways to reduce TNs for throwing weapons (still waiting for canon stats on Smartball technology).