Crystals, on their own, are a form of magical reagent. It should be entirely possible, and perhaps even trivial, to prepare a crystal as an inanimate vessel for a spirit. Quartz crystals in particular deform ever so slightly when an electrical current is run through them, are easy to come by, and are available in a variety of sizes ranging from the size of the smallest bone in your pinky finger all the way up to "bigger than a roll of quarters". This is an important point, so bear with me.
Spirits, as far as I am aware, can be instructed to react by casting a spell when a certain constant in the environment changes, or a stimulus is applied to a vessel they inhabit. As quartz crystals react readily to electrical current, they're ideal for this thought experiment. SO!
- Start by acquiring a revolver. Modify it with an electronic firing mechanism, and a smartgun system if you feel like it.
- Next, acquire a stock of quartz crystals and shell casings appropriate to the caliber of your firearm. Be sure to modify the casings in such a way as to conduct the electrical charge of the firing mechanism into the crystal fitted into them. This should be a simple process, involving two insulated conductors and little else. Then, befriend a mage that can bind spirits to inanimate object vessels - or if you are a mage yourself, learn how.
- Prepare each "crystal bullet" as an inanimate object vessel, and get a spirit into at least enough of your brand-new exotic ammo to fill your revolver. Be sure to load the spirit in question with a combat spell, like Stunbolt or Manabolt or what-have-you. Ensure the spirit has enough services available to cover these instructions: "Wait until the crystal you're inhabiting is exposed to an electrical current and simultaneously deforms. When the this condition is met, cast your combat spell at the first thing directly visible to the crystal on the physical plane."
- Optional, if the spirits you're using have enough services to be 'shot' more than once: "Return to the beginning of these instructions if you have tasks remaining."
- Load one of your experimental spirit-bullets into your electronically-fired revolver. Pull the trigger. See what happens.
Is this one of those ideas that would make a GM want to slap me stupid(er) with an entire published library of SR books all at the same time, or could it actually work without blowing up in my face? Keep in mind, I'm still not entirely clear on how spirits work.