Old fashioned bullet

Hi, into my possession has come a rimless brass bullet. The underneath is stamped KN 11a or 12,there is Naval crown with an old fashioned M embossed on the cartridge,the actual bullet is stamped Sterling Silver.
Are you able to give me any info on this & what type of gun this came from.
Many thanks

https://www.iwm.org.uk/history/look-inside-the-princess-mary-gift-fund-1914-box

The cartridge case should be .303" In this instance, apparently manufactured by KN - Kings Norton

The description given by the IWM is slightly inaccurate in saying that it was a brass tube - they were fired cases.

KN (Kings Norton Metal Co. Ltd, Abbey Wood, Kent)
1914 Princess Mary Christmas Tin, Bullet Pencil.
These are quite collectable, particularly if the pencil is still present.
Sam3