Lewis and Clark only had one air rifle. it is a fascinating story (well it is to me, to each his own)
http://beemans.net/lewis-assault-rifle.htm
This is a very comprehensive article on the rifle. I don’t remember if it was .41 or .45 calaber, but I have full confidence that someone here will JUMP to the opportunity to fill me in. It is a 22 round repeater, and also fascinating because being an air rifle is not regulated in so many jurisdictions of this great country.
The air reservoir was pumped up to 800 PSI so, ouch, this thing will put your eye out.
Yes, Lewis and Clark attributed the rifle to saving them from Indian fights more than once when they demonstrated its fire power. The English used air rifles, similar to the one Lewis and Clark had, against Napoleon, they had snipers using them. You can buy air rifles today of .50 caliber and that pump up to those large PSI numbers but I am not sure of the laws governing them. The feds, of course, think they are too silent and should not be used. They have obviously never heard one of the new pellet rifles which are almost as loud as a .22. I am sure a .45 or .50 caliber would make quite a racket.