There weren’t any AR-15’s on the Lewis and Clark expedition. But Lewis’ Girandoni air rifle served the purpose of showing firepower at the time. We’re looking at half the congresscritters wanting to ban magazines that hold more than 10 rounds – and the Girandoni was a 20 round repeater. The whole story is here: https://www.beemans.net/lewis-assault-rifle.htm and it’s worth reading. To convince you, I’ll bring in a few high points.
The Journals of Lewis and Clark that I read in my youth were incomplete – actual publication of the “whole story” didn’t come around until 2001 – so little was in print about Lewis’ air gun. The Girandoni came from Austria. About 1,500 of these air rifles made it into the Austrian army, beginning around 1770, and all were surveyed out of commission in 1815. We know that Lewis bought it in Pennsylvania, and that he wasn’t fully proficient with it as he started the expedition: “Thomas Rodney, who was a day visitor to Captain Meriwether Lewis while he was traveling down the Ohio River at Wheeling, Ohio in September of 1803, contains a tiny passage which has caused new thinking about the Lewis airgun. The passage reads:
Visited Captain Lewess barge. He shewed us his air gun which fired 22 times at one charge. He shewed us the mode of charging her and then loaded with 12 balls which he intended to fire one at a time; but she by some means lost the whole charge of air at the first fire. He charged her again and then she fired twice. He then found the cause and in some measure prevented the airs escaping, and then she fired seven times; but when in perfect order she fires 22 times in a minute. All the balls are put at once into a short side barrel and are then droped into the chamber of the gun one at a time by moving a spring; and when the triger is pulled just so much air escapes out of the air bag which forms the britch of the gun as serves for one ball. It is a curious peice of workmanship not easily discribed and therefore I omit attempting it.”(Beeman’s excerpt of Thomas Rodney’s letter.)
Other articles describe how Lewis would show that his rifle could fire 20 shots without reloading when he met with natives – and that they really weren’t sure that his was the only repeater. For years, I believed the expedition was armed with model 1803 rifles – until I got to TSJC, and the college library showed the first 1803 was completed in October. It looks like Lewis highgraded the Harpers Ferry arsenal for fifteen 1792-94 contract rifles – and he may have had some cut down by arsenal smiths, as his journals refer to “short” rifles. Authorized more than the 15 men he had rifles for, the record suggests that the rest brought their model 1795 muskets along. With Clark bringing a 36 caliber rifle, the expedition definitely did not have standardized weaponry.
Again – the Beeman article is worth reading – click on it, and enjoy reading how the most unusual gun carried by the Lewis and Clark expedition was discovered and identified by its history of repairs.