The Army is working to switch from the 5.56 mm ammo to the 6.8 mm next generation squad weapon. This is a future weapons program that includes the MG 6.8mm which we've acquired some new animations to. They plan to pick a winner of the bid and finish the switch by 2023. Sig Sauer, Textron and General Dynamics are all still in the running. 

This weapons program was started to give the US Army increased lethality at greater ranges. The ammo for these future weapons are all incredibly unique since they feature hybrid cases. This includes plastic ammunition, polymer ammo as well as a steel / brass casing.