Volley gun
The Ribauldequin was a medieval version of the volley gun. It had its barrels set up in parallel. This early version was first employed during the Hundred Years' War by the army of Edward III of England, in 1339. Later on, the late Swiss army employed it.
Bullet
The first use of gunpowder in Europe was recorded in 1247. It had been used in China for hundreds of years. The cannon appeared in 1327. Later in 1364, the hand cannon appeared. Early projectiles were made of stone. Stone was used in cannon and hand cannon. In cannon it was eventually found that stone would not penetrate stone fortifications which gave rise to the use of heavier metals for the round projectiles. Hand cannon projectiles developed in a similar fashion following the failure of stone from siege cannon. The first recorded instance of a metal ball from a hand cannon penetrating armor occurred in 1425. In this photograph of shot retrieved from the wreck of the "Mary Rose" which was sunk in 1545 and raised in 1982. The round shot are clearly of different sizes and some are stone while others are cast iron.
The development of the hand culverin and matchlock arquebus brought about the use of cast lead balls as projectiles. "Bullet" is derived from the French word "boulette", which roughly means "little ball". The original round musket ball was smaller than the bore of the barrel. It was loaded into the barrel first, just resting upon the powder, and later using some sort of material as a wadding, between the ball and the powder as well as over the ball to keep it in place, it held the bullet firmly in the barrel and against the powder. (Bullets not firmly on the powder risked exploding the barrel, with the condition known as a "short start".)