AN IMPACT GUN ADAPTED TO DEFORM THE TUBULAR END OF A FASTENER SECURED TO A SUPPORT, INCLUDING A PLUNGER MEANS SUPPORTED FOR RECIPROCATING MOVEMENT BY THE BODY PORTION OF THE GUN HAVING A SPECIALLY DESIGNED HEAD PORTION ADAPTED TO ENGAGE THE INNER EDGE OF THE FASTENER AND DE FORM THE TUBULAR END RADIALLY OUTWARDLY AND TOWARD THE SUPPORT. THE HEAD PORTION OR ANVIL IS INITIALLY SEPARATED FROM THE PLUNGER OR HAMMER, AND IS GUIDED INTO CONTACT WITH THE END OF THE FASTENER BY A PILOT SUPPORTED FOR RECIPROCATION WITHIN THE HEAD PORTION. THE METHOD DISCLOSED HEREIN INCLUDES DISPOSING A SUPPORTING MEMBER WITHIN THE TUBULAR FASTENER AND IMPACTING THE FASTENER END.