7.62×25mm in the context of "Full metal jacket (ammunition)"

A full metal jacket (FMJ) bullet is a small-arms projectile consisting of a soft core (often lead) encased in an outer shell ("jacket") of harder metal, such as gilding metal, cupronickel, or, less commonly, a steel alloy. A bullet jacket usually allows higher muzzle velocities than a lead alloy cast bullet without depositing significant amounts of metal in the bore. It also prevents damage to bores from hard steel or armor-piercing core materials.