My magus wants to make "missing component" potions. The idea is that they would allow the creation of "grenades" that only work on specific creatures or in very specific situations. Please kindly put away any assumptions about the Medieval Paradigm while reading this post. If you've read any Dresden Files you should be fine.
The original idea, pretty specific to our unusual Saga, is a substance we can coat our grogs' ammunition in that is completely inert in day to day situations. The coating is specifically designed to inflict extra damage on Red Court Vampires. Originally I'd conceived this as an extra +5 Ignem damage but, on further consideration, I feel the best way for the potion to "recognize" Red Vamps is to be made with Vis harvested from them, which is Perdo. So a Pe Co potion effect for +5 damage or so.
A second similar idea would be to make a Pe Te potion effect (again, coating ammunition) that causes a bullet to explode like a torpedo when submerged in ocean water (or in brackish water in general, making it usable in estuaries).
Just how far out there is such an idea, in your opinion, WRT to how the rules on Hermetic magic and labs work?
My magus has an Affinity with Terram; might I be better off enchanting batches of slugs and shots using a variant on the potion rules instead of using actual potions?