Some 50-110 Express load data from Mike Venturino's "Shooting Lever Guns of the Old West".
Bullet: NEI# 500-300 GC .509" 314 gr. Note: Original factory lead bullet listed as 300 grain solid, or hollow point
Powder Charge
Accurate Arms XMP 5744* 40.0 gr
Goex Ffg 105.0 gr
Goex Ctg. 110 gr
DKT jacketed softnose .510"
Accurate Arms XMP5744* 40.9 gr.
*Emphasis mine: SR 4759, if available, is very close in burning rate to 5744. Load data will be very similar.
Venturino noted that the rifling rate of twist in the 50-110 Express was 1:60"
You may already have case length info, cartridge OAL, etc. if not, I can pass that information along as well.
Hope this helps.