It's not really the friction causing the most heat on the GC. It is the pressure. When a metal or anything else is compressed, it creates heat. The greater the compression the greater the heat produced. The pressure creates compression of the GC and the shank. Also, the higher the psi of the load the more heat is generated by the burning gas. Thus at 50,000+ psi it appears there is sufficient pressure on the GC to create sufficient heat. The paper is an excellent insulator and does not convey heat well and probably its compression does not create the same heat. Additionally, since PP'd bullets are not shot at 50,000+ psi successfully we don't really know if the paper is or would be burnt or not.