However, you have not mentioned the drawbacks to caseless ammo....
1) The cartridge case extracts a majority of the heat generated by the propellant when it is extracted and ejected.
2) The cartridge insulates the propellant from the heat of the chamber.
3) The cartridge case provides breech obturation.
(1) and (2) have cause all previous caseless designs submitted for military testing to fail the minimum cook-off requirements. (3), as many a gun bunny may know, makes the breech of caseless (or bag) gun more complicated and increase the maintenance requirements. After so many rounds, you have to clean the obturation ring and breech seal.
Also, brass, steel, and aluminum are pretty tough, the self-contained, metallic cartridge is a water-proof, durable, almost "wooden" object, it's hard to beat...