With the move to smokeless powder there were still many old guns out there that were proofed for black powder loads only. The “Nitro for Black Powder” meant that the cartridges were loaded with smokeless powder/cordite and were proofed for these black powder rifles but only up to the pressures of the original BP loads and not the later Nitro Express loads. On the bottom right hand specimen can be seen the L C on the headstamp, mening it was also known as a Light Cordite load