The rifles of that time had a very decent fire rate but this steam machine gun had a fire rate of supposedly 400 rounds per minute which is ridiculous for that time. But this weapon wouldn't be here if it had succeeded. The gun is massive and its lethality is nothing compared to its gunpowder powered competitors and its effective range is no where near as good. There was only one of these built so all of these statistics are coming from an episode of mythbusters that built a version of it and had very interesting results.
The reason I think it failed is due to its size and relative ineffectiveness. It is a great idea but a little late to the game. If a modern steam powered machine gun were made today i really doubt it would have any effect. with modern body armor and large armored vehicles this weapon would be turned to scrap metal in a matter of seconds. I do have to hand it to the confederates though it is an ingenious idea but it didn't win them the war. Thank you again and next week, Pepperbox guns.