I have posted this before and it is really a good formula to use. I have a 50 Cal TC Hawken and I am using 75 grains and it is accurate and clean burning. Every gun is different but this may save a little time and powder.
I found this a long time ago on a black powder forum. This is the formula that British officers used on the old gun ships to ensure they had enough powder for troops and the ships cannons. I have used it and it is pretty darn accurate. To check the accuracy, when I sighted in my 50 cal Hawken I started at 55 gr and worked my way up and low and behold I settled on 75 gr. Pretty much dead on for this formula.
I figured the British Naval officers had to have their act together or the outcome of a battle would end terribly wrong. You can try it out and see if it comes close to what you are using. No harm done if it isn't good enough for you to use.
Formula for figuring out black powder load for any firearm.
diameter of ball X diameter of ball X length of barrel, divided by 9 = optimum powder load.
50 Cal Hawkin powder load
.495 X .495 X 28 ÷ 9 = 76.2
