The Girandoni military air rifle

An example of this gun was carried on the Lewis and Clark expedition. The amazing ability to fire off 20 rounds accurately in mere seconds impressed the Indians so much they called it "big medicine" and decided to leave the expedition in peace after a friendly demonstration.

Lewis demonstrated the Girandoni at each Indian encounter which allowed the party to remain unmolested throughout their journey. Only one person died during the entire two year expedition and that was due to natural causes.

The territory of the United States was more than doubled due in no small part to an ingenious Austrian air rifle

The Girandoni military air rifle is a butt reservoir air rifle with a rifled bore. This conical iron air reservoir serves to hold a supply of highly compressed air and to act as the rifle’s buttstock. An external tubular magazine, along the right side of the barrel is described as holding 20 lead balls which are gravity fed to a transverse loading bar at the breech end of the barrel.

After moving a ball into firing position, the gun is cocked by pulling back on a hammer-like cocking lever. The force of the mainspring is converted into a straight line motion as the wedge pushes the striker against the forward end of the air rereservoir's valve. The tip of the striker pin forces open the valve and releases a short blast of compressed air to force the ball up and out of the barrel. This all can be repeated so rapidly that all 22 balls could be fired in less than a minute. The original air reservoir pressures topped at about 800 psi. Reloading of the tubular magazine was accomplished using 20 round speed loader tubes.

This amazing weapon could launch a lead ball, of about one-half inch diameter, of about 210 grains to a muzzle velocity of at least 500 fps for about 117 ft. lbs. of muzzle energy.

This gun is and it's unprecedented firepower were developed at the end of the 1700s. 1500 of these weapons were issued to the Austrian Army where they remained in service until about 1810.

They were eventually pulled due to the difficulty in recharging the air cannisters (it took 1500 pumps of the issued air pump to fill a cannister) and gunsmiths of the time were ill equipped to repair the guns. There also had to be teams with wheeled pumps and wagon loads of pre charged cannisters to keep soliders supplied in the field which turned out to be a logistical problem.

The June 2006 issue of American Rifleman has a fascinating article on this gun and its role in the Lewis and Clark expedition.

I was also able to find much more detailed information at http://www.beemans.net/Austrian%20airguns.htm