I was poking around looking at the pages on the evolving Black Horn 209 site and noticed they now have a PDF file of cartridge loads using the powder and rifle/pistol primers. The length of the BP must be the reason for the 209 requirement for muzzleloaders.

http://www.blackhorn209.com/files/pdf/Black%20Horn%20Cartridge%20III.pdf

I don't recall off the top of my head what the conversion factor is for weight vs volume but they do have loads in 45 and 50 caliber that have up to 71 grains by weight behind some rather large bullets (some over 500 grains). I guess this shows they are continueing to test the powder for different applications and bullet sizes. I didn't see a chart for muzzleloaders but the site is still "under construction".