Hornady 308 Win. 165-Grain GMX TAP Barrier: Hornady's TAP Barrier turns cover into concealment. The 165-grain GMX TAP Barrier is constructed of a monolithic material and has a double cannelured design to reduce fouling and pressure. The Gilding Metal eXpanding (GMX) round penetrates auto glass, sheet metal, and other conventional barriers with exceptional weight retention while still delivering superior terminal performance on the other side.