I'm not a machinist, just a home tinkerer. But just for fun, I tried my hand at making a reloadable .41 rimfire short case for an 1870s Colt 3rd model derringer. After machining the case, I drilled an offset chamber for the .22 blank used as a primer. I test fired it in the little Colt and it went BANG
Next up is to load it with black powder, a 126gr heel bullet and go to the range