It is absolutely SOP with .303 British ammo unless it is marked as MkVIIz. All Mk 7 (or Mk VII) is cordite-filled with the card wad. You are seeing the wad jammed into the case as it was filled before being necked down. Imagine that nowadays with OSHA! Filling a primed case & then squeezing it down!
Allan Quatermain: “Automatic rifles. Who in God's name has automatic rifles”?
Elderly Hunter: “That's dashed unsporting. Probably Belgium.”