I never really thought of the term "Sweet Spot", but it is an apt description. I was just told it was the point of best accuracy. Sweet Spot = Best Accuracy.
My teacher was an engineering professor who hauls 7 or 8 guns to Friendship each year for individual matches, and often returns with medals. He is very good at the analysis and "whys" or loading and shooting muzzleloaders. His advice has always proven sound in my testing.
Some points he shared:
A slow twist (roundball twist) may need more powder to get an accuracy load, but the "Sweet Spot" is wider in terms of powder charges.
A fast twist (bullet twist) will often have its "Sweet Spot" at a lower powder charge, but the "Sweet Spot" will be narrow.
Start with a charge equal to the ball diameter (40 grains in a .40 for example), and go up 5 grains at a time looking for the "Sweet Spot". You will know that you are approaching the accuracy load when the sound changes from "boom" to "CRACK!" That has proven true for me.
My experience has been that I have never found an accurate load below the Sweet Spot.
I have never found a Sweet Spot accuracy load below a mid-level charge. All three .50s here shoot small groups at 50 yards with 70 to 75 grains of 2f. Just worked out that way.
Within the limits of my eyes and open sights, I don't think 75 grains of 2f in a .50 would have any trouble taking a black bear or deer. I don't think it would be ethical for me to shoot much past 50 yards here in the SE. Maybe there is another accurate load way up the ladder of charges somewhere, but why would I need it?
Some barrels have a much wider Sweet Spot than others. Green Mountain barrels are very prevalent at Friendship, and in my experience have a very wide Sweet Spot. My Bergmann .50 Hawken is especially this way. I have another .50 with a well-known maker's barrel that only has a very narrow Sweet Spot, and only then if I use wet lube. You'd think it was a very fast twist bullet barrel (it is not), but it has the same Sweet Spot charge of 72 grains of 2f.
I do wonder what folks are using as patching that doesn't blow up with huge charges?
In my brain, the only hunting load worth considering is the accuracy load. This is for me personally. I don't live out west where shots are long for a muzzleloader. I think I owe it to an animal, and the accuracy gives me a confidence edge. I did a lot of hunting on grey squirrels, often with an air rifle mostly due to noise. There is no margin for error with an 800fps .177 pellet, so accuracy is essential.
Just thinking out loud here and I am sure others have loads they use that work for them.
I also realize what I think of as accuracy others may differ on. I am always striving for shots touching at 50 yards. I have run into folks who say, "I can hit a paper plate, good enough."
The photos below show groups I shot at 50 yards from Green Mountain barrels. The top one is the first three-shot group from the Hawken after I bought it (yes I changed that rear sight). The lower photo is a five-shot group from another rifle with a GM barrel. The shot to low right is the first shot out of the barrel, the next four in one hole. The first shot outlier may have been the monkey on the crank too. The rifles may do better than these groups, but my eyes cannot see any better than that. Yes I consider these "cheater" targets, and no I could not produce these groups on a squirrel in a tree with my current eyes. Not enough contrast.
God Bless and best wishes, Marc