Lewis and Clark had a secret weapon when they went on their famous exploration of what is now known as the Western United States. The secret weapon Lewis and Clark carried on their expedition was a late 18th Century .46 cal. twenty shot repeating air rifle by Girandoni. This rifle was first used during the Napoleonic Wars. If you enjoy history, you might like to read Undaunted Courage by Stephen Ambrose, the book that is mentioned in the video.