This essay takes a look at early firearm development up till the 1500’s. It is a fascinating read.

Certainly, the first uses of gunpowder are psychological – loud bangs and sausage-shaped rockets snaking across the battlefield to terrify men and horses. This is the role we can see for the fire lances of 1132. It is a short step from here to the early handgonne. I believe that while the bamboo pellet throwers of 1259 did not use true gunpowder, they certainly were a first application of the principle of using burning gases to throw a projectile…

Serpentine lock firearm, 1411

More here.