Carpenter crews were setting a bulkhead panel. The panel was being lowered into position when it got hung up on a horizontal water stop cut out on a 2x6 guide bar. The injured employee pushed on the panel to clear the guide. Upon doing so, the slack from the cable was taken up and the panel shifted. The employee's left-hand fingers were pinched between a set form and the bulkhead panel resulting in a partial amputation of the left ring finger involving the tuft of the distal phalanx.