There's a considerably lower velocity , for sure- a regular rifle would have had around 1,000 feet per second, an airgun perhaps 700. But that's still pretty effective out to 100 yards with a .46 caliber ball. The Austrian snipers could also reload 20 times, without having to stand, just by pointing the muzzle up. There also would be no smoke or flame, and low noise. Perhaps they weren't as lethal as a .69 cal. musket, but they could certainly damage. It was not surprising Napoleon threatened to hang any soldiers captured with one.