The Marine Corps and Army are developing new caseless and case-telescoped ammunition that, when partnered with a new light machine gun also in development, could significantly cut the burden on troops in combat. And perhaps more significant than that, in the coming years this revolutionary ammo could drive production of the Corps’ next service rifle.
Back to the story though, the concept of caseless ammo is not new, and the challenges associated with it are well known. First thing to understand is that when a brass cased cartridge (or plastic shotgun hull) is fired inside of a chamber, it seals off the expanding gasses at the chamber end which aids in velocity of the projectile down and out the muzzle. Caseless ammo has to overcome this hurdle. Secondly, when the case is ejected, it takes heat with it -- which it's good to expel the heat and all, but it also is mechanically complicated to have an ejection system in the first place, which is a major cause of malfunctions. So that part is a double edged sword. You may have heat problems (almost certainly), but you should have a huge boost in reliability since there's no expended case to eject, and less moving parts in the system. The remedy for the heat issue may be in the use of a modern propellant, and I have no idea on how they would tackle the gass-sealing issue.
The main reason though for caseless ammo consideration is a reduction in weight. This also is a double edged sword because, as veterans will attest, a reduction in weight in one area translates to an increase in weight in another. Guaranteed. You read it in articles all the time about "reducing combat weight for the poor overburdened Soldier," but that's all just a bunch of bullshit in reality. Somewhere, in a secretive and non-descript room in a huge five-sided building, some heartless yayhoo with an evil laugh has a magic number bayoneted to the wall that shows the total average weight an 18 to 20ish American male in good physical condition can carry for four days without dying from exhaustion, and they approve a certain amount of weight above that number. The upside is that you get to tell the Warrior that the reduction in weight will be filled with a corresponding increase in killing potential -- that will go over well, or at least much better than telling him or her that the weight will be made up for with sandbags or some other equipment -- batteries -- that won't be as useful for slaying enemies.
I'm all about caseless cartridges. In fact, I'd kinda like to try my hand at reloading them, considering my addiction and all. Instead of resizing brass cases until my fingers bleed, I could be molding my own rounds out of putty-like propellant on a miniature pottery wheel. . . . like in Ghost! It would definitely be better for my nails!