In the Napoleonic era it would have been a spherical ball.
It was in this trying situation, exposed to a galling fire of blank cartridges, and harassed by the operations of the military, a fresh body of whom had begun to fall in on the opposite side, that Mr. Pickwick displayed that perfect coolness and self-possession, which are the indispensable accompaniments of a great mind. He seized Mr. Winkle by the arm, and placing himself between that gentleman and Mr. Snodgrass, earnestly besought them to remember that beyond the possibility of being rendered deaf by the noise, there was no immediate danger to be apprehended from the firing.
'But—but—suppose some of the men should happen to have ball cartridges by mistake,' remonstrated Mr. Winkle, pallid at the supposition he was himself conjuring up. 'I heard something whistle through the air now—so sharp; close to my ear.' 'We had better throw ourselves on our faces, hadn't we?' said Mr. Snodgrass. Pickwick Papers (1836)
The word carried on being used, even when the conoidal Minié bullet appeared.