if you watched discovery channel than you probaly seen this
this spiffy little toy is called the OICW (objective individual combat weapon)The OICW can be a dual- or single-barrel weapon. The removable top barrel hurls 20mm high-explosive air-bursting fragmentation rounds over the heads of hidden targets more than a half-mile away. The lower barrel shoots NATO-standard 5.56mm ammunition. These "kinetic" rounds provide accurate single-round or suppressive fire bursts at distances up to about 500 yards. A single trigger is linked to both barrels, by way of a laser-guided electronic fire-shot system as sophisticated as what you will find on a modern tank.