I know I have a couple of good disasters in my memory banks, but the banks seem to be closed today.
A small but cringeworthy one, also involving a gun, that I ALWAYS remember: I was piano-conducting a small backstage band for Kiss of the Spider Woman, and one night the warden's gun refused to fire. After a few pathetic clicks, he finally shouted "BANG!" .. and the scene more or less went on.