As a bit of trivia for history fans, the Girandoni Air Rifle was a true innovation that virtually ruled out use of gunpowder. It began service in the Austrian army from 1780 to around 1815. On the plus side it had a high rate of fire, no muzzle report, and no tell-tale smoke (thus enabling snipers to deliver a silent death). Furthermore, it was the first repeating rifle of its kind, used a tubular magazine, and actually more advanced in technological design than the Henry rifle which appeared fifty years later. The rifleman could reload this weapon whilst lying down thus not exposing his position.
Sadly, there were certain impracticalities:
1. The detachable air reservoir (although capable of 30 shots) required 1500 strokes to refill.
2. The reservoirs were manufactured from hammered iron sheets and proved a difficult craft with tools during this period.
3. The gun itself was delicate and one slight breakage could render it useless.
4. Operating the weapon required a different process to its flintlock/gunpowder counterparts; snipers needed special training in order to use it.
5. Although deadly at 150 yards, accuracy was affected by a near-empty reservoir.
You can find more facts and statistics about this weapon on Wikipedia.
Robert Douglas