<< ...9mm is not a common cartridge for a revolver. >>
True, but Ruger managed to produce a couple winners. The OP's Blackhawk (with 2 cylinders) and my wife's SP-101 (using 'full-moon' clips). Both great shooters in a common cartridge...well, three in the case of the Blackhawk(.38 Spl, .357 Mag & 9mm).
I bought the 357 only version last month. I like it and it's fun. Ammo for 357 has gone crazy retarded (as high as $50 a box) around here, so I have shot mostly 38 spl thru it.
I did, however, pick up a spring kit from Midway for around $20, which included a 19 pound hammer spring and 40 ounce trigger spring, to lighten the trigger pull up some. I haven't shot it with the new springs in it yet, but test firing it seems to be a lot better than stock.