As for the MG mark I believe this indicates one of the small arms factories in Melbourne, Australia. Number 2 maybe?
I also seem to recall as a matter of interest that the Mk VII round differed from ealier types in that it was "tail heavy" due to an aluminium piece in the nose which although it was stable in flight (effects of the rifling induced spin) it tended to tumble on impact increasing the wound balistics. Not very nice but not illegal due to the full metal jacket and the fact that it did not fall into the category of a frangible missile (expanding or dumdum)
I hope this helps
Edit; Oops should have read the whole thread! Seems I have repeated the comments of others, sorry!