My experience with air rifles has been limited to the spring powered BB gun I had as a child. The Sherlock Holmes stories speak of compressed air weapons being used by big game hunters, but I never looked into them. The fact that such a weapon was on the Lewis and Clark Expedition pretty much exhusted my knowledge of the subject.
A couple of days ago our son, Matt, sent me the following link.
It seems my handwritten link is not working. If you do a goggle search under "Lewis and Clark air rifle" several links will come up. This will include a couple of videos, including the one I was trying to send you to.
Sorry, still working bugs out.
The Girandoni held abilities not obvious to the untrained eye. The shoulder stock was a reservoir that held enough pressure for about fourty shots. A tubular magazine on the side of the barrel held 22 .46 caliber lead balls.
They were loaded by way of a spring loaded, sliding block with a single cavity. When the block was pressed the cavity would move from the breach to the magazine where a single ball would drop in, then back to the breach and the weapon was ready to fire. Imagine a 22 round, .46 caliber rifle that could be emptied in less than a minute.The Girandoni used a different set of tool than gunpowder weapons, carried in this case. It included a bullet mold, spare parts, and a 'bicycle pump' for charging the reservoir. It took about 1500 strokes for a full charge.
Meriwether Lewis was impressed enough with this weapon to purchase it out of pocket. He used it in a most effective manner on the Expedition to the Pacific. I found this U-tube video to be most interesting and very enlighting. It's well worth the time to look, and I hope you will enjoy it as much as I did.