The M829E4 is called the Advanced Kinetic Energy round, and belongs to a class known as APFSDS-T: Armor Piercing, Fin Stabilized, Discarding Sabot with Tracer. As the picture shows, the shell casing releases a penetrator sabot dart, which flies at extreme velocity to punch through enemy tank armor. The tracer element makes it easy to see the round in flight.
While manufacturers like Rheinmetall use tungsten alloys for the APFSDS dart, American rounds use alloys of similarly-dense depleted uranium (DU)...
http://www.defenseindustrydaily.com/Next-Gen-120mm-Tank-Killer-ATKs-M829E4-AKE-06995/
While manufacturers like Rheinmetall use tungsten alloys for the APFSDS dart, American rounds use alloys of similarly-dense depleted uranium (DU)...
http://www.defenseindustrydaily.com/Next-Gen-120mm-Tank-Killer-ATKs-M829E4-AKE-06995/