A launcher for propelling projectiles out of a barrel using compressed gas. The receiver includes a grip with an opening for receiving a compressed gas cartridge. In some embodiments, the grip includes a door movable between an open position that allows the compressed gas cartridge to be removed from the opening, a closed position that retains the compressed gas cartridge in the opening, and an activation position where the door cooperates with a gas transfer mechanism to pierce the seal of the compressed gas cartridge to release gas. The door can be closed without piercing the seal, but a greater force can be applied to the door to pierce the seal.