Abstract: A rapidly-adjustable butt stock assembly comprised of a butt stock, a buffer, a slot cylinder, a key cylinder, and keys. The butt stock has a cylindrical recess with key grooves longitudinally therein for receiving the slot and key cylinders. The key cylinder is rigidly attached to the buffer. The slot cylinder has at least one longitudinal slot with a plurality of transverse slots extending therefrom. The key cylinder carries one or more keys, which keys extend through the key cylinder and the slot cylinder and into the key grooves of the butt stock. To adjust the length of the assembly, the user rotates the slot cylinder so that the keys rotate out of the transverse slots and into the longitudinal slot of the slot cylinder thus permitting the key cylinder to move axially with respect to the butt stock.