I have made some calls to knowledgeable people. This is only happening with one brand of sabots and I am told it is a combination of a slightly over sized sabot that is also made of a material that is not very slick and a solid cooper slug. The theory is that its building up heat as it goes down the tube. The molds for making sabots can be a lot amount of money, guess they figure it is cheaper to replace the occasional barrel than pay for a new mold. Same theory as the Pinto gas tank.