.38 rimfire black powder cartridges out of an ancient top-break revolver. Only about 80% fired on first try. Usual solution: Rotate and try again.
Very moderate recoil, lotsa smoke, lotsa smell.
I seem to recall the cases were copper, not brass, but memory fades from so long ago (late 1960s). Also might have been .32 rimfires, but .38 sticks in my mind. This was up at the Boulder Co city dump, which is now the south range of the Boulder Rifle Club.
Terry, 230RN