Where to start?

At the beginning I suppose but which beginning, the round? My work with this cartridge or the arms race that started it?
I am going to dip in and out of history to do this, as one wag pointed out "History its just one thing after another!"
So here I will borrow from others, Pathe News and Ian from Forgotten Weapons:

That is where I will leave this today, more to follow.

https://www.thefirearmblog.com/blog/2017/05/15/empire-strikes-back-recreating-legendary-280-british-7x43mm-round-guest-post/