The powder magazine stored ammunition below ground level for safety so that if powder exploded, most of the blast energy would go upward into the air rather than outward, protecting the fort and reducing injury to soldiers. In 1837 the United States Army was using flintlock muskets manufactured at Springfield and Harpers Ferry Armories. Black powder, which was highly flammable, was made from three ingredients: charcoal refined to carbon, saltpeter or potassium nitrate, and sulfur, in proportions of approximately 75 percent saltpeter, 15 percent charcoal, and 10 percent sulfur.