A rig crew was preparing the mast to lower during a rig down. During preparation to lay the mast over, the incorrect pins were removed from the “A” legs. The pins that connect the front leg to the rear leg of the “A” Leg assembly were removed instead of the pins that connect the front A-leg assembly to the mast legs. Once the mast was broke over the center of gravity point it was free to fall/pivot to the ground. No one was injured but the equipment was severely damaged.