Thought this might ease you pain......
just think what these guys are going through !!

7.62x51 on the left, for scale
6mm Lee
5.2mm Mondragon
5mm Sturtevant

7.62x51 and 6 mm Lee (Remington-Lee) I have heard of but the other two look like work shop "one-off" cartridges. Ivan

5.2mm Mondragon looks like it might be fun to try ... once
I bet the velocity of that animal might cause some temporal distortion if the theory of relativity is correct.
properly applied, you CAN get the 2 minutes of your life back from reading this

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it just needs more voltage

Mondragon sure looks "different" so I did a quick search and velocity is not that impressive - only 2600 ft/s. What's more impressive is that projectile is sitting on a piston ring ! (in your face reloaders )