Was it to be fired while still “buckled”?
If so, woe to the guy with a beer gut. Ouch!
BTW, it sticks in my mind that there was a Civil War-era design kind of like this. A black powder, derringer type weapon that fired out of the belt buckle. Something like that. I remember reading about it in an old library book about 19th century firearms. Might be have some of the details wrong, though, as I was very little when I read about it.
I remember the toy cowboy hat with the gun hidden in a trap door on the inside of the top of the hat.. SURPRISE!