How thick is round leather 1745 equivalent to flat leather

1745 leather, double folded, folded length of twenty centimeters or so, pull open to the full bow state, with eight millimeter steel ball, this time the initial speed of about seventy meters per second, this speed has been able to reach the traditional slingshot's highest hourly speed, flat leather 0.8 thickness, the same with the eight-millimeter steel ball, single-stranded pull open in the middle of the distance 80 -90 centimeters between the initial velocity of the launch is basically the same.