From the Warren Commission report.
Quote:The detailed autopsy of President Kennedy performed on the night of November 22 at the Bethesda Naval Hospital led the three examining pathologists to conclude that the smaller hole in the rear of the President's skull was the point of entry and that the large opening on the right side of his head was the wound of exit.148 The smaller hole on the back of the President's head measured one-fourth of an inch by five-eighths of an inch (6 by 15 millimeters).149 The dimensions of that wound were consistent with having been caused by a 6.5-millimeter bullet fired from behind and above which struck at a tangent or an angle causing a 15-millimeter cut. The cut reflected a larger dimension of entry than the bullet's diameter of 6.5 millimeters, since the missile, in effect, sliced along the skull for a fractional distance until it entered.150 The dimension of 6 millimeters, somewhat smaller than the diameter of a 6.5-millimeter bullet, was caused by the elastic recoil of the skull which shrinks the size of an opening after a missile passes through it.151
