Apparently, there's something called a 10mm Magnum. You can have a cylinder's chambers bored out to accept the slightly longer case of the 10mm Magnum.
A little too much of a good thing I think. It winds up trying to be the .41 magnum which was trying to be the .44 magnum which leaves that middle ground halfway between .357 and .44 still empty. Plus the 10 mm magnum brass I've seen was rimless.
Herter's .401 powermag was in the ballpark.
I get pretty close with .38-40 but I'd rather have straightwalled brass for carbide dies and I'd rather not push the .38-40 quite that hard.
