I shot 35 gr of 777 in the Ruger Old Army, and it kicks and hits like a 44 Special... It's hot stuff. I used a Wonder Wad under the ball. If you drop it to 30 gr, you might get away without a filler, but 25 grains might be too far in for the rammer to get the ball to the powder without cornmeal or such, or additional Wonder Wads. You want NO air space. In the Ruger, I also, without Wonder Wads, shot 40 gr of 777, and it was substantial.
777 gives the equivalent load to the full charge of bp in the old balloon head case, as a 45-70 balloon head held 70 gr of black, a modern solid head case only holds 60 gr. 60 gr of 777 is equivalent to 70 gr of black. It's something like 15% stronger. Yes, it weighs less per bulk (as does Pyrodex and Cleanshot) so you have to measure it by volume. There is a Pyrodex weight factor, published, but all the substitutes weight varies from lot to lot, so volume is the only reliable method.
Good luck. 777 cleans real easy, with MP7 or Ballistol. Water if you must, if Stainless, no problem.