Here are all the ones I can think of. Advantages, Weight savings, ammo weigh's less so more can be carried. Disadvantages, 1. Prone to "cook off" during prolonged firing. 2. Difficult to manufacture. 3. Expencive, even in mass production. 4. Fragile, since the powder IS the case it is prone to being gummed up by grease, grime, any solvent could destroy it as well as rain. 5. Can't be loaded by hand, the ammo can't be handled by hand, therefore all you have are preloaded mag's. If you have 3 mags with 10 rounds in it, too bad. You can't combine them in one full mag. 6. Limmited shelf life. As you can see, the disadvantages FAR outweigh the advantages. The only places I see caseless ammo having a chance is in aircraft cannons, where the enviornment is clean enough for caseless ammo.

The original gun planned for the F-15 was to have been a 25mm 6-barrel Vulcan type, using caseless ammo. But serious issues with the technology of the time arose: too difficult to manufacture a caseless ammo propellant grain capable of withstanding the Eagle's operating environments: temperate, hot dry arid desert, humid tropical, sub arctic (also the comparably arctic temperatures at high altitudes.) In the 1970s, they just could not manufacture a reliable caseless propellant "shell" that could withstand such a vast "environmental envelope"..

AFAIK, when the 25mm Vulcan finally did show up,(on the Harrier II) it was a plain old cartridge-firing job. Even the F-22 and F-35 use the 20mm M61A1..

What is caseless ammo? It makes me think of the old muskets where you have to first toss a bunch of powder down a barrel and then ram home a ball. Or big arty with its bags of powder. Is the powder somehow formed into a shape that holds the shell?

The gun on the Harrier is a 5-barrel GAU-12B/A 25mm system (often referred to as Equalizer, not Vulcan. And there was also a 4-barrel model called Blazer.) The gun for the F-15 was to be a 6-barrel system (don't have the designator, though this could be the gun referred to once as "Terminator", seriously.) Scholar, caseless ammo is basically a hardened but fully-combustible solid propellant grain, in which the projectile is fully- or semi-recessed into the material, and upon firing, all the propellant is consumed with no empty casings to contend with. Some MBT s used "semi-combustible" ammo, in which a propellant section was composed of similar material, and after firing, only a "base stub" remained, which held the initiator charge. Basically, just picture a bullet cartridge without the brass wrapped around it and a chunk of solid propellant instead of powder..

has anything been done with those yet? I heard about the concept and it looks promising

Crosshair - why is it so expensive? If anything, I would imagine at least the weapon using it would be cheaper and more reliable (no need for jamming-prone mechanisms to eject spent cases).

How would these work? I have never heard anything about that.

It is more expencive beause the propelants themselves are expencive. You ahve to make the rounds stable enough so they don't go off in handling, but volitle enough to ignite in the gun. Like trying to make a candy bar with an edible wraper. Sure it could be done, but it wouldn't be cost effective. Second such a weapon would NOT be more reliable. What happens when you have a misfire. No easy way to get the round out. The brass/steel/whatever cartrage expands and seals the chamber then the gun is fired so that no propelelant gases leak onto the shooter/rifle mechanisim, no easy way to do that with a caseless ammo. All the caseless rounds that I know of are also tend to be brittle and prone to absorbing any liquid they come into contact with (oil/water/blood). If you want a more reliable weapon for US troops, then get rid of the retarded gas system that the M-16 uses.

Ok, that makes sense. So if not caseless ammo, how could traditional small arms be modernized in the near future? Or have we reached the peak of small arms development with pieces like XM-8?