ROTFLMAO. I will forgive you.
Ok then.
5.2x68mm ruben.
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That’s the beast. Your article is slightly different to mine and was worth the read, very interesting.
Here is mine…
This was one of the earliest small calibers rounds. It was designed by the Swiss Colonel Rubin in 1894 for a semi-automatic rifle to be built by the Swiss, the rifle being a design by Mexican Manuel Mondragon. This was the first semi-automatic rifle to reach production (although by then chambered for conventional 7 x 57 mm Mauser cartridges. It was made in limited numbers (about 4,000 total), and after Mexican default on the contract the remaining rifles ended up being sold to Germany where they were used as aircraft weapons during World War I.
The projectile has a cupro-nickel clad steel (CNCS) jacket and brass ring at the base.
According to the Rubin’s patent, the piston ring around the base of the bullet allows for more energy to be used to drive the projectile than a conventional design. The piston ring is stopped at the shoulder while the projectile continues down the barrel. The projectile is 31 mm in length and had a muzzle velocity of about 800 m/s (2,600 f/s).
Visible on the outside of the case is a smooth cannelure. The piston ring sits on this indentation. Presumably the case is necked after the projectile assembly has been seated.
Note: because of the chemical composition of early smokeless powder, many of these rounds have started to deteriorate inside.
The powder used in this section is of a similar time period and shape, but not original to this round.
The headstamp is ‘POLTE MAGDEBURG’
Reference: Military rifle & Machine Gun Cartridges by Jean Huon. p. 32
Now if an old bloke like @GUN-DMC can guess it how come you didn’t?
Yes he probably used one when it was being tested but that’s no excuse. 
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Yeah I’m crusty but not actually that old. Unless you ask my kids, Lol!
Now that is a frightening thought from both sides LOL.
.475 bishop short magnum?
No mate, not that one.
Is it a 5.45x28?
Nope bigger than that
7.62x25?
Bigger still
Mmm 8x22 Nambu
Nope not that.
Although it is an 8mm /7.92 round.
Lol, not the 8mm Japanese?
I helped restore a very beautiful stalking rifle in this caliber a couple of years ago, the owner still has it and shoots goat and fallow with it. Would hate to think of it’s value if he sold it. The military application of this cartridge was groundbreaking, Cheers.
Looks a bit short…Kurz?
Not map.
Yes there is kurz in the name but you’ll need to be more specific.
Yes it sure was a revolution when it came out, looks a lot to me like it may have inspired the 7.62x39.