Rocketman:
In Winfer's book on Holland single shot rifles, he provides the same information that CFWs quoted from SBDR along with reproductions of the original Holland prints. The BP load used a paper patched bullet.
Winfer also offers a modern smokeless powder load for the .450/400-2-3/8:
230 grain bullet
30 grains 3031
Large Rifle primer
Velocity = 1700 fps.
I have no experience with this chambering so you are on your own. This load does seem in keeping with other Nitro for Black loads I have seen and the velocity is in line with the original loads. FWIW, even back in the early days of cordite the smokeless loads produced lower pressures for a given bullet velocity than did Black Powder. At least as long as you didn't take the ammo to India or Africa...
Glenn
