>>64083537
>IIRC some army guys set out to create a better long range cartridge than 5.56
The actual story is that the M855 zipping through skinnies at close range phenomenon was found to be caused by "fleet yaw" and out of several bullet diameters put through JSWB-IPT testing 6.8mm was the one least affected by it.
When compared to 6mm, 6.5mm, 7mm and 7.62mm the 6.8 offered the best combo in terms of reliability, accuracy and terminal performance. So the whole thing was about close quarters fighting first, and figuring out the rest afterwards.
What followed was an issue with the SPC chamber specs being submitted with incorrect dimensions to SAAMI spec not once but TWICE, meaning that 6.8 SPC cartridges loaded to the originally intended pressures showed signs of overpressure like primers popping out. In the end most factory loaded ammo was underpowered and even though alternate chambers were designed for it, by then it was too little too late.