I don't get how literal some people are trying to make these guns lol Like you have to actually be injected with a syringe bullet to get a heal. Like in Resident Evil Outbreak you would load the specialty gun with anti-viral pills and shoot your friends to heal them lol we just accepted it as a game mechanic.

I don't believe my AST heals are INSIDE the person i'm casting it on. It's just around in swirls that recover HP.
Not to mention the "bullet" could easily disperse on the outside of the person kind of like when a projectile hits the Protect/Shell spells in cutscenes etc and you're helping their own aether recover their HP.

ranged have infinite ammo in this game. If you want to get literal then we'd have to go back to FFXI crafting and rationing our ammo and if you run out better hope your hand 2 hand weapon is enough to pull you through an encounter. I could see a mix of both Alchemist and using this type of gun, like when you attatch plantfood to a garden hose lol Mix various concoctions and spray your team in a recovery cone or aoe.