Abstract: A projectile firing weapon is disclosed having a simplified construction and a consequent increase in reliability. The trigger and firing mechanism are completely contained within an easily removable and replaceable cassette which may simply be dropped into a cavity in the weapon's stock. The entire barrel assembly may be attached to the stock by a single bolt and a pivoting attachment. The pivoting attachment allows the ready replacement of the barrel assembly or the ready replacement of the firing mechanism actuator cassette should either of them malfunction. The stock and hand grip may be formed of a single piece to further simplify the construction of the weapon.