I need the actor to be able to threaten the crowd and the gun helps sell it
If you want a gun to fire as a startle, contact any area civil war re-enactors. They often volunteer for our Haunted Hayride. We offer to pay for the powder, wadding and firing caps, but they refuse any payment. Muzzle loaders can and are used to great effect as a startle scare, but safety and responsibility are paramount.
That being said, I would highly recommend not "threatening" or pointing an actual firearm at anyone, including other actors. That is a surefire (pardon the pun) way of getting sued, arrested, or having the firearm confiscated, even if it is simply a starter pistol. The muzzle loader rifles used by the civil war folks are capable of firing projectiles, so they are never pointed in the vicinity or at anyone...period. I have seen first hand how far the wadding can fly with a simple 50 grain, non-projectile discharge from a muzzle loader. These should always be pointed up and away from anyone. There is also the risk of hearing loss if fired too close to a crowd.
It is not worth the risk of liability, injury or death to wave a firearm at or near anyone. The person holding the gun can also be charged with threatening or reckless endangerment if a person really does feel threatened by a gun. Yes, even in a haunt. Like it or not, with the number of highly visible mass shootings recently, people can be very or even overly sensitive to guns being used this way. I live exactly 12 miles from where the Sandy Hook Elementary School shootings took place last year and the principal that was killed was a friend of ours. I still have no problem around guns and do own my own, but we will not be using any gunfire in this year's Hayride, both out of respect for the community and honestly, for fear of civil or criminal liability.
Yes, I am a lawyer, and no I have not stayed in any Holiday Inn Express.
Eric