The "right" load is the one that the gun shoots best. Sorry to have to turn the question around, but that's really the way to get to the right load.
Sam Fadala did a lot of test of many different black powder guns, looking to document the "optimum" load for each. He got many different answers, but the one theme that I saw in all that work was that the maximum load was almost never the best in terms of accuracy. The type of powder, the type of projectile, how well the load is installed, the amount of fouling in the gun, many, many things affect the results. And in the limit, what is also clear from the experience of many people is that what's good for my Pietta 1851 Navy Yank with a steel frame in .36 cal is different for my Pietta 1851 Navy Rebel Army with a brass frame in .44 cal, and will likely also be a little different for your Pietta/Tranditions 1851 (?) Navy (?) in .44 cal with a brass/steel/whatever frame.
How to find out? Crow_feather said it first: start out shooting 15 grains, a minimum of 3 shots but not necessarily more than 5, then shoot, say, 18 grains, the same number of shots, then go up to 20 grains and so on up to where the ball won't fit anymore. Do all this from a bench rest, with the same type of powder and type and size of projectile each time, and at a short enough range that you are certain of hitting the target every shot. And always shoot the exactly same sight picture. The idea is not to hit the bull in the center but to shoot consistently enough that differences in the loads become apparent. Keep track of the size of each group, and it will soon become apparent what load your gun likes best: the one with the smallest diameter group that you can shoot. With that powder type and projectile size and type. Rest assured it will be different if you change either. Maybe not much, but it will.
By the way, some of us would like to see you load powder, then a felt or lubed wad, then the ball and finally some Crisco or other gel type lubricant, or perhaps substitute Cream of Wheat for the felt wad in an amount large enough to bring the ball up to the chamber mouth... Whatever combination you choose to try, just do it the same each time until you settle on the best powder/ball combination for your gun.
A lot of work? Yep. Good excuse for lots of shooting too.