A gun is an aimable weapon that launches projectiles at high velocity, or a device that resembles such a weapon used for other purposes (e.g., glue gun). The term is also used for types of artillery with long barrels that fire at a relatively flat trajectory.
For handguns, long guns and historical cannons the projectile is a bullet, shot by explosives (gunpowder), but it does not contain explosives itself.
For modern artillery the projectile is a shell, containing explosives.
Technically speaking, the projectile is the weapon and the gun is the weapon platform, although with the use of bayonets and rifle butts as clubs, the double usage of the word could be forgiven.
Types of guns:
Manufacturers: