An Air Gun of the Girardoni Type
The air gun illustrated in this animation is 48.5 inches long overall, including a 32.8 inch barrel. The total loaded weight is nine pounds. The 51 caliber barrel is rifled with 12 grooves having one turn in the length of the barrel. The magazine has a capacity of 20 lead balls. Each air-rifleman in the Austrian Army carried two spare buttstock reservoirs and four refill tubes of rifle balls.
The breech-loading mechanism did not permit the use of a patch, which in a muzzle-loading flintlock served partly to hold the ball in the breech until the weapon was fired. Therefore the balls for this gun had to be molded with extreme care. If too large, a ball would jam in the barrel; if too small, air escaping around it would diminish the muzzle velocity. If Lewis carried a repeating air gun, this need for time-consuming precision could be one reason why he apparently used it only for demonstrations.
This animation is based on measurements and photographs of an authentic Girardoni repeating air rifle in the collection of the Tower of London. Through the cooperation of the staff of the Royal Armouries, the specifications were secured in person by Geoffrey Baker and Colin Currie of England, who then built a working replica for study and testing.1
A Reservoir and a Pump
An Austrian air-rifleman's assistant recharged the buttstock reservoirs from a large mechanical pump on a horse drawn wagon by attaching the buttstock pump to a similar foot plate on the pump. If Lewis's rifle resembled an Austrian army weapon, he could have stood on the foot plate and pumped up and down–as with a modern bicycle pump, although filling an air gun reservoir would have required a great deal more work than that. Approximately 2000 strokes, or more than 30 minutes of nonstop manual labor, would have been required to charge the reservoir of a Girardoni to the maximum working pressure of as much as 1,000 pounds per square inch.
With thanks for information and advice provided by Geoffrey Baker, William K. Brunot, and Michael Carrick. Animations by Bob Gilman; directed by David E. Nelson.
1. Geoffrey Baker and Colin Currie, The Construction and Operation of the Air Gun, Vol. 1, The Austrian Army Repeating Air Rifle (London, England: Privately Published, 2002).
Funded in part by a grant from the NPS Challenge-Cost-Share Program.