I have a couple of Hawkens that would no doubt stand a 150 grain charge. The Mountain Men considered a "standard" charge to be half the weight of the ball, and a "double charge", used for bear, buffalo, etc., was the weight of the ball-up to 230 grains of powder in a .54!! And, contrary to current belief, 19th century black powder was NOT WEAKER AND LESS EFFICIENT than the stuff available today! A lot of it was better!! However, most guns shoot more accurately with less than 150 grains, and a flatter trajectpory is of no value if your group size is measured in feet!!

Keep yore powder dry!!