I'm surprised nobody got to this sooner....
You might want to try the same amount of powder and seat the bullet with NO airspace or even slightly compressing the powder and you'll be fine...of course make sure you are at the correct total cartridge length.
For true BP, for example only, in .44 Russian, I use 20gr by volume of Goex 3f under a 240 gr bullet.
In .45S&W for my Taylor's, I am using 20gr by weight (25gr by volume) of Hodgdon 777 in 2f, under a 200 gr bullet. It seem to work for me, pleanty of bang, smoke and clang!
Good luck, be careful, please let us know.