Yes I know one should shoot the heaviest powder charge they can and still maintain good accuracy
I'm not sure that is a viable rule-of-thumb. I think that's a
modernism brought about when cartridge shooters began to return to using the patched round ball and muzzleloaders.
I know from direct observation that 70 grains of 3Fg will send my .530 ball through a deer standing broadside, out to 110 yards. I get acceptable groups when going as "hot" as 90 grains, which gives me merely 27 ft lbs more energy on the chart provided by galamb, and according to Goex gives me 270 fps higher velocity... but the 70 grains is the best accuracy, and I don't percieve the recoil nearly as much. The amount of force needed for my patched round ball to transit a broadside deer is the same for both loads..., the energy and velocity retained upon exit is a moot point once the work is completed.
The problem with the discussion is that we need an updated serious study of the patched round ball, as the study of the PRB stopped because the conical and the cartridge were invented.
Some of the most respected hunters of the time period of the end of the round ball and the introduction of the conical bullet report that the round ball, though lighter was superior. Some combat veterans reported the same thing. This was based on their observations.
Now on paper the energy from a conical is much higher than a round ball, so the question would be why does the patched round ball, when fired at the same distance at the same velocity, seem to take better effect on a game animal or a human?
This question seems to be answered in
The Sporting Rifle and Its Projectiles by Lt. James Forsyth, 1867. Forsyth had the option of patched round ball or conical, and from years of experience on big game, and dangerous game, would only use the patched round ball.
Forsyth was part of the "whompability" club, probably due to his experience coming almost exclusively from India. His parameters for his rifles, however, were to be able to shoot out to 200 yards, with
as flat a trajectory as he could achieve so he went for very large powder loads. This eliminated his having to learn how to adjust his sight hold for longer range shots (beyond 100 yards) or for the use of adjustable sights. YET..., he admitted in his book that while he wanted a rifle that he could depend upon out to 200 yards, in his personal experience he had not had to fire beyond 100 yards, and the vast majority of his shots were well under 100 yards. He surmised that would be the experience of big game hunters in other parts of the world as well. Sounds like the same distances at which most of us harvest our game, does it not... 100 yards or less?
LD