Join Date: Sep 2008
Location: Bavaria, Germany - the center of 15th and 16th century gunmaking
From aspects of science, and especially chemistry, we know that, with fine dust-like blackpowder before ca. 1600, saltpeter is volatile and such "meal" powder will generally not explode any longer than some 30 years after it got mixed.
In the case of grained 18th or 19th century blackpowder, I would basically recommend being careful.