Indy - you're right about the drum on the Gatlings. They were post-Civil War and the Civil War Gatlings used the stick magazines. I don't remember if they were on a tripod in the movie though.
I know the NY Times Gatling wasn't fired but it was supposed to have been prominently displayed. It's kind of like the SF Vigilantes. They posted their best marksmen on the rooftop to protect their HQ from being torched by arsonists. That alone deterred the threats from being carried out. I guess it's the Big Stick that never has to be swung.
BlueTrain - there was one American bolt action gun that was available during the Civil War. The Greene bolt action was made but never issued. Greene himself became a general during the war and was the defender of Culp's Hill at Gettysburg. A modest man, he never bragged about his accomplishment but National Park Service Historian Emeritus Ed Bearss remarked that Little Round Top and Culp's Hill were like two bookends. If either fell, the Union line would have collapsed. You'll see a statute of Greene on Culp's Hill when you visit it.
Vigilantibus et non dormientibus jura subveniunt. Molon Labe!