WWI Shell marking ID ?

I know we have a multitude of collectors on here, and whether we all like to admit it were historians. For me the charm of history was always more intriguing than the coins and was evident at a young age when I would quiz my grandparents “what it was like growing up during the war”? Naturally, for you curious lot they looked back with fond memories but lessons learned. I’m not sure what my grandmother's parents did but my great grandad on my grandad sailed in the merchant navy throughout the war ensuring the empire and our island remained intact. As such there are coins from the era from Fiji, Australia and many more.

Now I'm done with the trip down memory lane I’m wondering if any of you kind folk could help me understand some more about this shell ?

Check out this web site. I'm sure it will help. Nice 6 pounder.

https://hatchfive.wordpress.com/category/shell-casing/