I don't personally own a cartridge open top. But I shoot cowboy action with someone that uses two open top Uberti Colts that are chambered in .44-40. The guns have stood up well for him.
One thing that all the Italian open top guns seem to have in common is that the arbor is too short to fit the barrel correctly. The intent of the design is that the nose of the cylinder arbor is supposed to seat against the front of the barrel. The wedge holding these points firmly in contact. The length of the arbor when seated in this manner sets the cylinder gap.
But it's pretty standard, from all I've seen, that the arbors are way too short and what happens is that the wedge is used to "spring" the barrel into place and it becomes important to set the wedge to attain the proper cylinder gap.
There are a few methods for fixing this issue. Some fit the arbor or barrel with a threaded set screw that is adjusted to the right position so it bumps into the other piece and sets the cylinder gap. Some just use a drop in washer of the proper size. I've done that to get by. But it's way too easy to forget there's a sized shim washer in there and let it fall into the grass. Some like to fit and solder or otherwise attach a nose button on the arbor so the shim remains firmly in place. This last method is the one I prefer. I did it for my buddy on his two open tops and I've done it on my four cap and ball open tops. In fact here's a link to the thread where I detailed the job;
http://www.thehighroad.org/index.php?threads/buttoning-up-the-open-tops.785288/#post-9980127
I'm going on at some length here so that if this is your first open top that you realize that some additional work will need to be done before the gun will be truly set up well and provide the optimum reliability and accuracy. I have no idea why the Italians can't get this one little thing right. Even if they charged a little more so it was that would be fine. But it is what it is and if you want the best out of an open top it really should be done.
Oh, as for the choice of caliber? It would be a little odd for sure. After all .45 Schofield was a S&W caliber. And if there is one thing that history shows us it is that there was no love lost between Sam and the team of Horace and Daniel....
On the other hand it may well be that the smaller cases would seal better with the usual fairly light charges used in such guns. And if there's one thing I know for sure it is how badly cowboy action loads soot up the outside of .45Colt cases. The smaller case might just aid in reducing this small issue.
