I wasn't in any way sarcastic or negative, just thought that due to wording I misinterpreted your message.
As to differences - yes, even in a given caliber (although I meant it in broader way). Hodgdon has performance data both for rifle and handgun in 44. Many powders are used in performance data for handgun yet aren't considered for rifle (too fast, not much gain)
The idea would be to find a powder dense enough (to meet limited case capacity) yet slow enough (to take full advantage of extra inches)
This discussion makes me believe that it might be impractical to undertake the project, at least at this time. I'll probably still experiment with different pressures in 1680.
Crosshair: yes, heavier bullet is a plus. Unfortunately, it also introduces issues with slower rate of twist (restriction #2 in first post) Just in case life wasn't easy enough