Really good information in this thread, thank you for the responses and feedback. After looking at the hornady manual and ballistics by the inch, for my 4.75” Blackhawk I am probably looking more for a ~900fps load for the 300gr xtp instead of the 1000-1050fps I had originally stated. As others have pointed out, in such a short barrel I will be climbing pretty high into the +p realm with the heavy bullets at that velocity. Probably not necessary.
Based on the feedback I think I will try to work up two loads.. a 300 xtp @ 900 and a 265-280 WFN @ 950. I should be able to use 2400 powder with a little room to build up or down if needed.