Meriwether Lewis, of course, could not carry out the President’s wishes alone. He enlisted the aid of his friend, Captain William Clark who put together an expeditionary group known as the Corps of Discovery.
In addition to Clark’s black slave, York, the party numbered over 45 men. Many (about 27) were young, unmarried soldiers. They would be gone a long time. Life, as they knew it, would be very different on the journey which began in St. Louis.
President Jefferson wanted to be sure the men had enough supplies. Lewis needed to purchase not just what he and his men would need. He also required "Indian Presents" to trade during the trip. While the expedition ran out of luxuries (like salt, liquor and pigtail tobacco), the Corps never exhausted their basic supplies of rifles, powder, ammunition, paper and ink.
One rifle - above all others - was important for the expedition. It was used by Lewis in a very special way.
Historians believe the gun was a Girardoni repeating air rifle which had been employed in the Napoleonic Wars. Lewis used it not to kill, or hunt, but to impress Native Americans as the Corps of Discovery traveled through various tribal lands. When he fired it, Lewis wanted people to be in awe of the rifle's power.
Native Americans called it a "medicine gun," as Lewis noted (on January 24, 1806) in his journal:
Our air gun ... astonishes them very much, they cannot comprehend its Shooting So often and without powder, and think that it is great medison [medicine] which comprehends every thing that is to them incomprehensible. (Original Journals of the Lewis and Clark Expedition, 1804-1806, Volume 4, page 11.)
Lewis never let on that his rifle was unique among all the others which the Corps of Discovery was using.