Caseless ammo on the horizon?

Yes, caseless ammo has been around for a couple decades, but it always has been experimental, at least as far as combat use is concerned. The problem has always been durability -- while caseless ammo weighs far less than a round with a brass casing containing the primer, the powder and the bullet, as it does away with the casing, caseless ammo has so far failed to pass the test when it comes to the banging around that comes with carrying ammo into combat and using it there.

There is a possibility those problems have been  -- or at least are being -- overcome:

The U.S. Marine Corps and U.S. Army agree they may have finally found a caseless ammunition design that will work reliably in combat and be much (37 percent) lighter than conventional 5.56mm ammo. Caseless ammo is not a new concept but you need the right materials and right design to make it work. It’s all a matter of getting the right tech and the right design.

The effort is driven by the need to reduce the amount of weight soldiers and Marines carry into combat. Combat loads, including pack, body armor, weapon and ammunitition, typically weigh 70 pounds or more for a patrol of any duration  Efforts to reduce the weight of food and shelter elements continue, but gains there are incremental. No one has found a way to reduce the weight of water. That leaves body armor, weapons and munitions. Kevlar doesn't weigh much, and many soldiers and Marines already decline to insert  the "chicken plates" -- heavy ceramic plates intended to be inserted to protect the chest and back from heavier caliber ammunition than the Kevlar is designed to stop -- because of the weight factor.

Which brings us back to the weight of the weapon and its ammunition. The Army has been working on it for several years:

Meanwhile the U.S. Army completed development of a new LSAT (Lightweight Small Arms Technology) 5.56mm machine-gun in 2012. But this new machine-gun was tested using two types of lightweight ammo and it wasn’t until now that one of those lightweight ammo designs reached the point where it was ready for combat testing. The LSAT machine-gun weighs 4.27 kg (9.4 pounds) compared to 8 kg for the current M249. Moreover, the ammo for the new machine-gun is 37 percent lighter as well. Thus the new machine-gun, with 1,000 rounds of ammo, weighs 13.9 kg (30.6 pounds), which is 40 percent less than an M249 with a thousand rounds. Moreover, the new ammo takes up twelve percent less space. Developers are working on caseless 5.56mm ammo that will take up 40 percent less space.

The problem with caseless ammo always has been that it doesn't hold up well under combat conditions. Without a brass case, propellant has a disturbing tendency to separate from the bullet under rough handling. That pretty much renders caseless ammo useless. It would appear that Army testing may have resolved those problems:

In early 2012 eight LSAT machine-guns and 100,000 rounds of the telescoped ammo were delivered for army troops to actually use and passed field tests. At this point it became possible to use the same technology for a new assault rifle. While LSAT passed muster with the troops and the realities of use in a combat zone by 2012 most of the fighting was over. The new machine-gun will be much appreciated by infantry operating in Afghanistan, where the machine-gunner is often lugging his weapon and all that ammo up steep hills. But back home there was less enthusiasm, and money, for a new generation of assault rifle and light machine-gun.

The ammo used in the test is not caseless - "telescoped ammo" basically has a plastic case. Nonetheless, plastic weighs less than brass, and apparently caseless ammo is making progress. The guys toting the ammo into combat will doubtless appreciate the effort.