An automatic pistol is safer than a revolver for use on horseback. There is no putting to half-cock but only slipping the safety on or off.
If the horse begins to plunge, slip on the safety at once, in fact at any indication of trouble with the horse put on the safety.
Do not slip off the safety till the instant before firing and slip it on the moment you have fired.
As you cannot shoot blank ammunition out of an automatic pistol you will have to use a single barrel pistol for teaching a horse to stand fire.
Be very careful not to scorch him or shoot past his eyes as that will make him always apt to flinch.
An underbred horse is better than a blood horse as a rule for shooting off, but when you do get a thoroughbred who will stand fire, as he has more courage, he will stand fire better than any other horse, and his paces are easier, especially the canter and gallop.
A handy polo pony makes a good shooting pony if it stands fire, as it is used to starting, stopping, and turning.