The Girandoni air rifle was in service with the Austrian army from 1780 to around 1815. The advantages of a high rate of fire, no smoke from propellants, and low muzzle report granted it initial acceptance, but it was eventually removed from service for several reasons. While the detachable air reservoir was capable of around 30 shots it took nearly 1500 strokes of a hand pump to fill those reservoirs. Later, a wagon-mounted pump was provided. The reservoirs themselves, made from hammered sheet iron held together with rivets and sealed by brazing, proved very difficult to manufacture using the techniques of the period and were always in short supply.
In addition, the weapon was very delicate and a small break could make it inoperable. Finally, it was very different from any other weapon of the time and any soldier using it needed to be highly trained.
The Lewis and Clark Expedition used the rifle in the demonstrations that they performed for nearly every Native American tribe they encountered on the expedition. When they saw multiple shots fired with no smoke they had to be impressed. Perhaps impressed enough not the attack the explorers. That could explain why the Expedition was indeed, never attacked.