.303 FN Grenade cartridges

These three FN .303 Grenade cartridges apparently all have the same designation of ‘H Mk 7z’ but the variety of black staining to the cases and colouring of the wax seals would suggest that the rounds are different in some way. It may simply be that they were intended for different customers and were marked in accordance with their wishes.
They are marked ‘F N 50’, ‘F N 52’ and ‘F N 53’ respectively.

The earliest H.7z supplied to the British were unmarked, and that is what your FN 50 looks like.

After that they had the lower half stained black and I think those two just represent two different years of production. I have noticed similar variations.