Before the 5,56mm there was the 224E2 Winchester designed to be used in a larger M1 carbine design. Also the 222 Remington Special which did become the 5,56mm. Interesting is that the 224E2 Winchester could be fired in the AR-15 chambered 222 Rem Special.
Early test cartridges are interesting and the last photo shows the British 4.85x49 mm cartridge which was an attempt to improve the performance of the 5,56mm a few years later.
The 4,85mm Tracer is difficult to find as well as the AP Attachment 113155Attachment 113156Attachment 113157
