The 31 would work for a caliber. However all the common 31s are built on the small frame which makes it a bit harder to hold and shoot accuractely. Too bad no one makes a copy of the Manhatten revolver. You could build your own by using and 1851 and lining the bore and chambers to 31 caliber. With decent sights it would be a fun revolver, but with decent sights, the Navy Colt is a fun revolver. Even with issue sights it isn't too bad.