oshinari Namiki's comment Nylon has suppleness which Fluorocarbon do not have. If you use thick diameter of Fluorocarbon more than 20lb, the line has stiffness and it prevents from extending a  casting distance. “Machineguncast” is aimed low elongation and high abrasion resistance while it is supple as Nylon’s property and keeps low specific gravity. We have applied each different line qualities for maximize the advantage. If the fishing line becomes thicker, it naturally loses its suppleness. Therefore, we adopt the best materials to each range in order not to feel differences in use.