The 10mm Magnum cylinder would be nice, but be prepared to dish out the coins for brass. In all my years of dealing with the 10mm (early 1990), I am yet to find a spent 10mm Mag brass or used for sale. Star Line does sell them which is good, load data is slim but is available.
But to gain the most of the cartridge 8 3/8" or even 10" barrels would be better for ballistic potential...
38-40 has some following in the Cowboy Action stuff...