Today’s invention is a magazine for firearms which allows the user to choose the kind of round to fire next (ie blank, high-charge,tracer, rubber etc).
The magazine would be filled with a number of different types of round, in order.
It would have a spring at either end, so that as rounds were extracted and fired, as usual, the remaining ones would be available to choose, by moving the magazine up or down. This movement could be controlled manually or motorised in response to a switcahable safety catch indicating which type to select.
This offers the possibility that eg a police officer could, without stopping to swap ammunition clips, choose to fire a warning shot or a rubber bullet, rather than have only lethal projectiles to fire.