I am getting so much conflicting information from burn rates of powders to the pressure of a given load.
Ultimately I am looking for load data from others who have loaded for this gun/ammo combo.

I took a peak, they mention low pressure, 12,500-13k max for the Webley. That’s even lower than the relatively low pressure 45 acp round.

A Google search brings up a fair amount, one could interpolate averages from that. Older manuals may have data specific, like they have with older trap-door 45-70 rifles.