Complex sentence: Concentration of the force into a smaller area was approached by replacing the single metal (usually steel) shot with a composite shot using two metals, a heavy core (based on tungsten) inside a lighter metal outer shell.
Split into simpler sentences: Concentration of the force into a smaller area was approached by replacing the single metal (usually steel) shot with a composite shot using two metals. A heavy core (based on tungsten) inside a lighter metal outer shell.