A weapon for firing a projectile is provided that includes a receiver within which is disposed a loading mechanism for loading and unloading the weapon. A feed system supplies the loading mechanism with ammunition and a firing mechanism releases the loading mechanism for loading and firing the projectile. A barrel is rotatively secured to the receiver and preferably includes a rifled bore that imparts a gyroscopic spin on the projectile and a rotational force on the barrel causing the barrel to rotate as the projectile is fired. In a preferred embodiment, the barrel is provided with a plurality of blades that capture air and generate airflow across the weapon and barrel to cool the barrel.