some years ago I checked options for reloading the 11.2 x 51 R Kropatschek-Heissig with BP subsitutes.
One idea was using Pyrodex, but after reading that it shall be as corrosive as regular BP I abandoned that idea.

I worked up a load using SR4759.

Another option I tried is 4198 as described by Ross Seyfried: 40% of the BP weight, plus Dacron as filler.