[@vietmyke][@The Angry Goat] Open fire comes from guns, and the flame that spurts from their mouth.  Without fire, guns would be ineffective...so it kinda makes you wonder what they're using instead of gunpowder to start with.

Open shooty is hilarious and somewhere I have something similar but I can't find it.  Ah well.

However, given that we are modern people in our world, with modern word usage, I suspect we are going to be using "fire" as a term for shooting.  Or we could just say "shoot" (not "open shooty", mind, but similar idea).  The fun question is if perhaps people wouldn't hold on to the "loose!" command from bow and arrow or sling.