Hey Mulehead, you'll get a lot more views of your post if you use the regular Black Powder forum instead of the Black Powder Help forum.

What is the rate of twist of the .54's barrel? A 425 grain conical is likely to be too long to stabilize well in a very slow twist. But it can't hurt to try. I would start with 70 grains of powder, then 80, 90, and 100. You may hit paydirt.