1. AN APPARATUS FOR HOT FORMING METAL BILLETS INTO PRESELECTED SHAPES AND COMPRISING A FEMALE DIE MEMBER HAVING A RIGID IMPERFORATE BASE FOR SUPPORTING A BILLET AND A PERIPHERAL WALL EXTENDING AWAY FROM THE BASE AND DEFINING THEREWITH AN OPEN END DIE CAVITY, A PRESSURE RAM MEMBER, MEANS SUPPORTING SAID MEMBERS FOR MOVEMENT RELATIVE TOWARD AND AWAY FROM EACH OTHER ALONG A PREDETERMINED PATH, SAID RAM MEMBER HAVING A PERIPHERAL WALL AND, UPON SAID RELATIVE MOVEMENT OF THE MEMBERS TOWARD EACH OTHER, BEING RECEIVABLE ENDWISE IN SAID CAVITY THROUGH THE OPEN END OF THE CAVITY WITH THE PERIPHERAL WALL OF THE RAM MEMBER SPACED FROM THE PERIPHERAL WALL OF THE CAVITY A SUBSTANTIAL AMOUNT MORE THAN OPERATING CLEARANCE FOR RECEIVING METAL FROM A HEATED BILLET IN THE CAVITY WHEN THE BILLET IS PLACED UNDER PRESSURE IN THE CAVITY BY MOVEMENT OF THE RAM TOWARD FULLY INSERTED POSITION, A METAL RESTRAINER DISPOSED INITIALLY WHOLLY WITHIN THE CAVITY AND HAVING AT ONE END AN OUTER FACE FACING AWAY FROM THE BASE AND TOWARD THE OPEN END OF THE CAVITY, AND SPACED FROM THE BASE AND OPEN END, AND AT THE OTHER END AN INNER FACE FACING TOWARD, AND SPACED FROM, THE BASE AND OPEN END SO THAT AT LEAST A PORTION OF THE INNER FACE CAN OVERLIE THAT PERIPHERAL MARGIN OF A BILLET IN, AND FACING TOWARD THE OPEN END OF, THE CAVITY WHEN THE BILLET IS BEING FORMED IN THE CAVITY BY THE RAM MEMBER, SAID RESTRAINER SUBSTANTIALLY BRIDGING THE SPACE BETWEEN THE PERIPHERAL WALLS BEFORE THE RAM IS FULLY INSERTED IN THE CAVITY, SAID RESTRAINER BEING CAPABLE, WHEN HEATED TO THE TEMPERATURE OF THE BILLET TO BE FORMED, OF DEFORMATION IN A DIRECTION AWAY FROM THE BASE BY PRESSURE OF BILLET METAL FLOWING IN THE CAVITY DUE TO PRESSURE EXERTED ON THE METAL BY THE RAM MEMBER, CONSTRAINING MEANS ON AT LEAST ONE OF THE MEMBERS AND POSITIVELY ENGAGEABLE WITH PART OF THE RESTRAINER, UPON SAID RELATIVE MOVEMENT OF THE RAM MEMBER ENDWISE IN THE CAVITY TOWARD THE BASE FOR PRESSURE FORMING THE BILLET, FOR RESTRAINING BODILY MOVEMENT OF THE RESTRAINER AND LIMITING MOVEMENT OF SAID OVERLYING PORTION OF THE RESTRAINER IN A DIRECTION AWAY FROM SAID BASE TO MOVEMENT TO DUE TO SAID DEFORMATION OF THE RESTRAINER AND TO A SUFFICIENT DISTANCE TO PERMIT DISPLACEMENT OF PART OF THE HEATED BILLET METAL FROM THE CAVITY INTO PART OF SAID SPACE, BY THE PRESSURE OF THE METAL OF THE BILLET BEING DISPLACED BY THE RAM MEMBER WHEN THE RAM MEMBER IS FORCED UNDER PRESSURE FULLY INTO THE CAVITY.