Movie Theater Another season of Gun Stories: Hard at work

When has the command "fire in the hole" been a command to commence fire with small arms or any projectile-launching weapon? I thought it was use to arm and setoff explosives? I think that is why the shooter was slow in shooting the mini gun because he was not sure the meaning of the command?
 
Actually pretty common, just getting everyone to understand it’s about to get loud. I’m the shooter, we’ve got several cameras running, so we often need to wait for everyone to get speed, time dolly moves and so forth. Sometimes I’m open ended, sometimes it’s a command fire problem. This take was open ended and a pause for another cameraman.