I have a New Model, and have put several thousand rounds downrange..... but they've all been .38/.357. I've never fired a 9x19 in it.
But, I can tell you this.... one person's experience with the 9mm in a Blackhawk will have little or nothing to do with what sort of accuracy you may get. Part of it is the shooter, and part of it is the firearm. It will most likely deliver better groups than you would get from a 4" autoloader, though.
I have both barrel lengths. I shoot a lot of 9mm through them for practice (CAS), and it feels like shooting 38s. The 9mm accuracy isn't that bad. The tightest groups are with the .357 of course. If shooting 9mm jacketed bullets work the best. If you don't reload, you can buy the cheap Wolf stuff, and have a lot of cheap fun.