I just found this information in the Feb 2005 Barnes newsletter and wanted to share it with fellow reloaders. "The X-cavity in the Barnes Triple Shock bullet has been redesigned to allow for controlled, reliable expansion over an even broader range of velocities. This same technology has also been incorporated into the entire Barnes X-bullet lineup, including the X, XLC, and TSX bullets. The main difference is the addition of 3 to 5 shallow grooves in the shank of the TSX design. These grooves reduce the surface area of the bullet in contact with the bore, and provide a place for material displaced by the rifling to expand into. This “relief valve” allows the bullet to travel down the bore without major distortion as the bullet is engraved by the lands and grooves. The result is reduced pressure and fouling, increased velocity, and better accuracy. Our results in the lab and feedback from thousands of customers all show that the TSX bullet is the most accurate of the three X-bullet designs."