CVA recommends a minimum of 50 grains, by volume, of blackpowder or blackpowder
substitute in your .45 or .50 caliber muzzleloader. The maximum load in CVA breakaction
guns, and any other CVA in-line rifle designated as a “Magnum” is 150 grains
by volume. This maximum load is generally known as the “magnum” load and is best
suited for pelletized powder due to the more efficient burning characteristics of the
powder pellets. Magnum loads of loose powder may be shot but are not recommended
because of their inefficient and incomplete burning of the powder. Some bullet
designs depend on the thrust of the powder charge to expand, or obdurate, the bullet
inside the bore for best accuracy. Loads under 50 grains cannot be depended on to
do this. In many cases lighter bullets are more sensitive to this than heavier bullets
and often require heavy powder charges to produce the best accuracy. For those
who wish to shoot moderate powder charges of 90 to 120 grains the heavier bullets
generally give better results.

sorry wrong link.......doesn't say you can't use 150grains loose, just says it is not recommended.....correct link below

http://www.cva.com/pdfs/Optima-Wolf%...n%20Manual.pdf