Honestly, I don't really know. Having not played the update, I'm not sure what the rarity of this new crafting juice is, but given how much inventory space it would take up if you had to stockpile it as ammo (and how tedious it'd be if you had to reload the guns after every shot), I'd imagine that the "guns" that would use it would be able to hold multiple crafting juices at a time as ammo, and each shot would use a portion of the juice. That, or the guns would automatically use whatever special juice was in your inventory - although that wouldn't resolve the issue of special juice taking up a load of inventory space.
Personally, I'd totally go for the "juice guns" being like water guns, where you'd fill the guns with crafting juice and spray out juice bullets of a certain kind affected by whatever you filled the gun with. Perhaps filling the "juice reservoir" of these super-soaker-esque guns with multiple kinds of juice would mix their effects, either allowing you to stack juice with a certain effect or create synergies of different effects that you prefer. Just spitballing.