The Winans Steam Gun was a steam-powered centrifugal gun used during the American Civil War, which used centrifugal (rather than gunpowder) to propel projectiles.
Similar in size to a steam-powered fire engine of the day, the gun had a menacing appearance thanks to a large curved shield covering its inner workings.
Its mechanism involved a shielded barrel that rotated up to 250 times per minute. Shot dumped into the top of the barrel rolled down into it and were held back by a spring-loaded gate that opened to allow one shot to be flung out per revolution of the barrel. Despite the effort invested in the project, it was unable to match the accuracy or power of the gunpowder weaponry of the time, and thus the steam gun project was abandoned.
The Mythbusters episode where they explored this concept was just uploaded recently! It’s a good watch if you’re interested.