i agree. I like to think of the black powder cartridges used after the civil war. A .45 cal gun shooting 70 grains of powder under a conical bullet was considered enough for the U.S. Army. Same for the .50-70. The Big 50 use at Adobe Wells to kill an Indian up on a ridge about 7/8 miles away was a .50-90 sharps. And, finally, Jim Bridger had a fixed powder measure made from an antler that threw 50 grains. He told a biographer that he used one " scoop " for deer and antelope, 2 scoops for elk, moose, and black bear, and 3 scoops for Grizzley Bears, in his .54 Hawken Rifle. Most shooters today would consider 50 grains under a PRB in a .54 Cal rifle to be very light. If you consider you are moving a 230 grain hunk of lead, it isn't.
Forget about maximum charges, and work on reasonable loads that are accurate. When you find lots of powder burning out the front of your barrel, you have reached the point of a maximum charge for that gun and load. Beyond that, the added weight of the powder justs adds recoil, without giving you any appreciable extra velocity out the muzzle. Use a chronograph to determine what is the best combination of powder, patch, lube and ball for your gun, and then stick with it. In my .50 cal. Flintlock rifle, I shoot 65 grains of FFg for my target work, and 85 grains for hunting. I am in the process of retesting my loads because I have started using over powder wads, which increase velocity in my gun, sothat I believe I will be able to reduce the amount of powder and get the same POI. How much I can reduce the powder charge is what I have to determine, but i am expecting it will be as much as 10 grains.