The Germans had been experimenting with a machinegun that fired caseless ammunition. Caseless cartridges would reduce the weight, allowing military personnel to carry more ammo OR carry other equipment in addition to their alloted issue of ammo. In war, weight is an issue.

The caseless ammunition would also free up the massive use of valuable brass & copper...these two metals are the favored material of the Western nations in the production of small arms ammunition. The former communist block countries favored plain in-expensive iron/steel (tin can material) for their cartridge cases.

Yes, it is. One of the most famous examples was the G11 rifle from Heckler & Koch. Although ill-fated, it worked, and proved the concept.

Shotguns don't use bullets. Do you mean without a case or non lethal projectiles? If so, yes they have caseless ammunition.

probably caseless ammunition - BUT the standard center fire cartridge works so well, is so cheap and so lethal - its why it hasn't needed improvement in over 100 years.

very caseless desk