Suggest you speak to Hornady and Hodgdon tech for guidance.
I would not load fast powder with a bullet of so much inertia as the jacketed 300 grain .44. Also, you may want to consider a cast 290 or 300 grain WFN or LFN.
Unless you want top possible velocity----with concussion grenade blast----which comes with magnum ball propellant H110/296, suggest you look for a medium burn rate in the range of HS-6, HS-7, Accurate #7, possibly Alliant Blue Dot.
Particularly speak with Ron Reiber at Hodgdon, if he is there. Reiber goes way back at Hodgdon, and further back at Hornady. Reiber knows handloading and pressure testing intimately, as well as being a handgun hunter and knowledgeable on silhouette.
Do not try for velocity with fast powder like HP-38 (HP-38 is Win 231). Pressure spikes wreck guns faster than slow rise. In fact, except for a light charge under a 240 grain or lighter cast bullet, I will not allow HP-38/231 in my .44 magnums.
Please make those phone calls.
David Bradshaw