In 1945, when the Bell X-1 was on the drawing board, there wasn’t a large body of technical knowledge on supersonic flight:
Bell’s engineers tried to fill in the data gaps on supersonic flight by observing objects known to fly at supersonic speeds — in this case, the .50 caliber round. Discussions with ballistics experts concluded that little was known about the aerodynamics of the round after it was fired, but since there was no question that it was stable at high speeds, its shape formed the basis for the X-1′s fuselage.
