Does anyone know the likely composition of a 17th century musket ball? (East India Company or British if relevant)

Odd question for a jewellery historian, I know, but it was an old practice to cast a diamond crystal in lead and then file that to determine the best size and shape that could be cut from it. One 17th century writer says that if you weighed the filed piece of lead and divided by 3 you would get the weight of the finished stone. That's out for pure lead (pb sg 11.34 relative to diamond at 3.51-2) but if we assume it was lead in some form that was readily to hand, it might be more accurate (its almost dead on for a 90% pb 10% sn alloy, for example).