¶ The conversion
1 gram of Black Powder FFFg = 0.6496684462 gram of 777 FFg
1 gram of Black Powder FFFg = 0.684639454 gram of 777 FFFg
¶ What does "F" mean?
"F" stands for fineness of the powder. For example, for the same equivalent mass of 777, the finer the black powder, or the more "F" it has, the less mass is needed to achieve the same effect. Therefore, although conversion from Black Powder FFFFg (the fineness often used for rockets) to 777 cannot be found, an approximation using Black Powder FFFg is sufficient.
¶ How is the Black Powder to 777 Conversion ratio calculated?
The original data used to calculate the conversion above can be found here . This chart provides the volume equivalent mass conversion from GEOX FFFg (which is Black Powder), to 777 FFg and 777 FFFg. However, according to multiple gunpowder forums as well as this other conversion chart used to cross-check the first one, 777 is 15% more powerful than Black Powder. Therefore, the volume equivalent mass of 777 should be reduced by 15% to achieve the same effect. Therefore, the conversion ratio from Black Powder to 777 is acquired by averaging all of the conversion ratios in the chart, and then multiplying the average conversion ratio by a factor of 0.85.