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The 4.73 x 33mm caseless ammunition used in the G11 rifle, shown disassembled. The components are, from left to right, the solid propellant, the primer, the bullet, and a plastic cap that serves to keep the bullet centered in the propellant block.

Caseless ammunition is firearm ammunition that aims to eliminate the metal case that typically holds the primer, or igniter, and the explosive charge ("gunpowder") that propels the bullet.

In typical caseless ammunition designs, the powder, primer, and bullet are held together with a binding agent. Other possible caseless systems might involve loading only projectiles and using a chemical or other explosive agent ignited electrically rather than mechanically.

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Caseless ammunition would have a variety of advantages. Removing the need to eject an empty metal casing:

• Allows a firearm to have a simpler, more reliable, and inexpensive design, by eliminating the components needed to eject casings.
• Allows the firearm to be better sealed against dirt and moisture, by getting rid of the ejection port (a port is still needed to extract chambered rounds, but not needed to be as big as a standard ejection port).
• Allows a firearm to be used by right- and left-handed users without modification
• Eliminates the hazard of ejecting hot, fast-moving casings
• Means that ammunition weighs less, allowing a soldier more mobility, or the option to carry more ammunition for a higher rate of fire and/or longer mission
• Reduces the cost of manufacturing the ammunition and avoids consuming raw supplies of metal
• Theoretically could be beneficial in sniping missions as the ejection of shells is a concern when trying to avoid being detected by enemy combatants.

The elimination of casings for heavier weapons is particularly attractive for military aircraft. Empty casings are problematic for moving aircraft: ejecting them creates the risk of foreign-object damage, and making provision to retain them requires extra space. The GAU-7 cannon was an attempt to implement this concept.

Caseless ammunition would be beneficial to infantry forces owing to its lighter weight. Its reduced weight would enable the entire logistics supply system, including the end-user, to carry much more ammunition. Increased supply would increase the practicality of weapons with a high rate of fire and of longer missions, while requiring fewer resources be devoted to supply chains. The lack of casing also would provide a tactical advantage to any soldiers in a hostile environment. A soldier could carry the same amount of ammunition as with regular cased rounds, but at a reduced weight to increase user endurance and mobility. For example, the caseless ammunition for the Voere VEC-91 weighs about one third as much as regular ammunition for the same caliber [1]. The lack of casings also makes such ammunition, at least in theory, cheaper to manufacture, since it would consume less material. Reduced cost would further enable greater use.

Caseless ammunition is still experimental, and has not been perfected. The current generation of binding agents, used to coalesce the powder and priming charge, can still foul weapons. Rounds of this kind of ammunition do not hold up well in wet climates or under the stress of combat conditions and tend to stress poorly in magazines and high rate of fire weapons, often breaking or otherwise disintegrating, as a result of being violently shaken around inside the magazine. The G11 used a floating barrel with a spring as a recoil buffer, presumably to mitigate this problem. A muzzle brake might also serve to reduce the stress on the ammunition.

An additional problem for fast automatic weapons is heat build-up. An advantage of conventional metal cartridges is that the casing absorbs a large portion of the waste heat of firing, protects the propellant from the heat of the chamber, and protects the chamber from being directly heated by the ignition of the propellant. Ejecting the hot, empty casing removes some of the ignition heat from the weapon, which helps to avoid "cook off" (premature firing of rounds due to a weapon's extreme heat). With caseless rounds, other means of reducing waste heat are necessary, especially in automatic fire. The approach taken with the G11 was to use ammunition which had a higher ignition temperature, which reduced the risk of cook-off. One possible solution would be to use an open bolt, which would prevent the round from entering the chamber until it is ready to be fired anyway. A historical approach to cook-off was water cooling, like with the M1917 Browning machine gun. Whether or not this would make caseless ammunition more reliable remains to be seen.

One of the first caseless firearm and ammunition system produced was actually made by Daisy, the airgun maker, in 1968. The V/L Rifle used a .22 caliber (5.5 mm) low powered caseless round with no primer. The rifle was basically a spring-piston air rifle, but when used with the V/L ammunition the energy from the compression of the piston heated the air behind the caseless cartridge enough to ignite the propellant, and this generated the bulk of the energy of firing. The V/L system was discontinued in 1969 after the BATF ruled that it was a firearm, not an airgun.

Several assault rifles have used caseless ammunition. One of the better-known weapons of this type is the G11 made by Heckler & Koch. Although the rifle never entered full production, it went through a number of prototype stages as well as field testing before being put aside in favour of more conventional firearms.

The first commercial caseless rifle featuring electronic firing was the Voere VEC-91.

Several notable weapons featured in the Alien film series utilize caseless ammunition:

• M41A pulse rifle
• M56 Smart Gun

Metal Storm

Heckler & Koch G11