The projectiles are typically solid, but can also be pressurized liquid (e.g. in water guns/cannons, spray guns for painting or pressure washing, projected water disruptors, and even flamethrowers. The first devices identified as guns or proto-guns appeared in China from around AD 1000.
See also: Guns N' Roses, Guns (essay), Guns! Guns! Guns!, Guns, Guns, Guns, L.A. Guns, Tracii Guns,