Cased ammo.
Maybe its time has come. The US Army is looking into it for use with a light weight machinegun and the Brits ARE using it for their Warrior upgrade program.
My focus is on the use of 40mm CTA for use on the AAV upgrade/ACV. We don't have to be wedded to the 30mm. The Brits have already done the work on the development of the round and it offers much greater kinetic energy. But what really caught my attention is that you can almost double the number of rounds carried by each vehicle and it allows for the weapon to be elevated beyond what you normally find in vehicle mounted main weapons. I'm thinking urban combat...plus having the ability to punch behind barriers with one round instead of using multiple hits.
Read about it here.