Built circa 1875, this powder magazine housed much of Fort Buford's ammunition supply and other ordnance stores, replacing an earlier partially underground magazine with stone-lined walls and an earth roof that poor ventilation and moisture had made unfit for ammunition storage. Its design reflected the need to keep ammunition dry and to reduce the risk of fire and explosion: ventilation was important, all nails and the wood floor were countersunk to prevent sparks, soldiers had to remove their boots or wear felt boot covers so hobnails would not spark, and munitions crates had screws and nails countersunk with the holes filled with putty. The metal door and thick walls were intended so that if an explosion occurred, the blast would go upward through the roof rather than outward, and the building was also made strong to protect its contents from theft. Because lanterns were not permitted inside, storage crates had to be clearly marked and easy to identify in dim light, sometimes by color coding, with each box labeled for the number and caliber of cartridges, the kind of weapon for which they were intended, and the day and place of manufacture. Tarpaulins covered crates against roof leaks. Not all of the fort's ammunition was kept here: some weapons and ammunition remained in the barracks, the Quartermaster's storehouse held some ordnance such as crates of firearms, and cannon munitions were stored in separate buildings. An inventory at Fort Buford in July 1877 recorded 590,993 rifle rounds, 129,513 carbine rounds, 15,081 pistol rounds, and 1,942 cannon rounds, indicating that this frontier post was busy with military activities of the time.