Here's some food for thought.

A .50 caliber gun shooting round balls over 85 grains of FFg Black Powder gets something around 1550 fps at the muzzle. That's works out to about 1020 fps at 75 yards (with 433 ft.lbs. of energy).

If the load is reduced to 70 grains, muzzle velocity will be about 1450 fps, and velocity at 75 yards will be 990 fps (with 409 ft. lbs. of energy).

So, going from 85 grains of powder to 70 grains reduces the powder charge by 18%, the velocity at 75 yards by only 3%, and the energy at 75 yards by only 6%.

To add to the dilemma, the trajectory for the two loads will be almost exactly the same, differing by less than half an inch.

Change the load to FFFg, or to Pyrodex, or to Triple seven and you get progressively higher muzzle velocities with an 85 grain load. But the reduction ratios work out about the same if you reduce the charge of each of those powders to 70 grains.

I know all this. So why do I still use loads in the 85 to 95 grain range in all of my round ball shooters.

It's called "Tim Allen Syndrome" MORE POWER! Or so your brain is telling you you have more power with a higher powder charge. Even when you KNOW you are getting little to no more impact poundage at distance. Aint kinetic energy fun!

I shoot whats most accurate. My flinter shoots 70gr 2fg and my 58cal perc. shoots anywhere from 80 to 120gr 2fg.

Accuracy would be the only reason when shooting those loads.
Can you run the numbers on a .58 shooting PRBs? Right now I am using 100 gr of FFg and getting phenomenal accuracy.

if its goex 2fg you are in the 1590-1604 range. At least thats what my .58 is shooting with 100gr goex 2fg, .020 patch and .570 ball.

100 grains of 2f in a .58 caliber according to T/C Owners Manual

1428 fps 1263 foot pounds of muzzle energy. Max load recommended is 120 grains of powder.

80 gr if 2f = 1302 fps and 1050 foot pounds of energy. More interesting is they claim 90 grains will be most accurate in rifles. Mine likes 100-110 grains in my GMB. But it does shoot very well with 90 grains. I just felt, like Semisane if I could push it that little bit harder, it would be more ... "deadly."

My results.

seems right for your .575 ball

Thanks guys. I would guess then with my renegade with the .58 GM barrel 1:70 on it and shooting 100 gr of Goex FFg I'm likely getting about 1450-1475 fps giving me upwards of 1275 FTLB of muzzle energy. That should be more than adequate for any whitetail out to 100 yards and I believe would also wreck a black bear's day.
I plan on using my .58 this coming week here in PA and later on in November for blackies.

depends on a lot of things, elevation especially. Im at 7300 feet and you guys are at sea level.