Gunpowder Facts

Originally, gunpowder was made by mixing elemental sulfur, charcoal, and saltpeter (potassium nitrate). There was no definitive opinion on the ratios, which changed dramatically from country to country and over time. The current balance of 75% nitrate,15% charcoal, and 10% sulfur was settled sometime in the mid-18th century in England. However, different countries had formulas that may partially account for their military success or failure. 

Changing the ratio of the ingredients also affects the rate at which the gunpowder burns and the amount of smoke it produces. Gunpowder produces much smoke, which can impair vision on a battlefield or reduce the visibility of fireworks. Incidentally, charcoal is not the only fuel that can be used. Sugar is used in many pyrotechnic applications.

https://www.nps.gov/casa/learn/historyculture/gunpowder.htm

https://www.nps.gov/articles/000/saltpetre-mining.htm

Fffg powder 7000 grains

7000 divided 125 = 58-60 rounds