Is this a proof round or a practice round. The head is made by VSM and dated 8/41, paint and stenciling doesn't look original to me. It looks like the head is originaly crimped to the case (dated 1944 and the primer is dated 1955)
I thought proof rounds were a factory deal though, I can't see a barrel leaving the shop for issue without being proofed ? If one was to burst on proof firing it would be a real mess in the water jacket on board. Is there no reference to this shot in a manual of the period ? This doesn't mean there aren't RN proof shot, I think though they are used on land, at sea the flat design would be unnecessary .