Bearing surface is a big factor. Its why our local idiots that thought they knew everything were getting over pressure from original X bullets. They did not look at load data. Simply used same as jacketed bullets. Those can compress some on firing AND for weight are shorter,hence less bearing surface. The more surface you have the more drag you create which increases pressure.

Although I've yet to directly compare TS and regular in the same weight, I can almost guarantee you that the TSX will give less pressure due to design of the driving bands. And if you went as far as to coat or moly them you might even eek out a bit more speed safely.