A loader device for loading BB-shot into a cartridge for air weapons includes a main body with a plurality of channels for housing respective rows of BB-shot balls and at least one holding member for holding the rows of BB-shot balls that have been introduced into the channels. Such loader device includes an elongate container with an open end and a closed end defining a cavity for storing a predetermined amount of BB-shot balls, wherein the open end has a temporary connection element for connection to the body of the cartridge, to provide simultaneous gravity loading of the rows of BB-shot balls into the respective channels of the cartridge. A cartridge for air weapons. A loader assembly including the loader device and the cartridge. A method of loading BB-shot into air weapons.