The July 2009 issue of Handloader Magazine (#260) had an article specifically for handloads in the medium frame ruger flattop blackhawk or the medium frame new vaquero. You should be able to purchase back issues or access back issues at their website (handloadermagazine.com). If that's not convenient, you can contact me by private message about sharing the data.
The article reinforced what Mr. Wright said. It kept the velocities at or below 1,200 ft/sec as a maximum. The 1,000 ft/sec, which you're hoping for was easily attainable.
I have a 4 5/8 and a 5 1/2 flattop in .44 special. I drive a 240 grain bullet at 1000 ft/sec as my everything-everyday load.
Last edited by hammie; February 24, 2013 at 09:53 PM.