BP guns are each unique so far as a best load.
I recommend increasing the charges by five grains at a time and shooting groups at 100 yards. My experience shows that as charge increase, bullet impact comes up and then drifts to one side and opens up. When the groups stop impacting higher and start to drift to the side and open up, you know that you have gone too far.
Otherwise, I like to shoot the heaviest possible charge for hunting. Muzzleloaders are not high energy firearms and don't usually drop deer like the high velocity rifle rounds. Instead I find that deer tend to run off a bit before expiring. To that end a bigger caliber and higher velocity help out.
