You are looking at two entirely different animals.
The JDJ, with it's "strong rimmed case", would not be an effective cartridge in today's select-fire weapons.
Secondly, the "new" 6.8 cartridge is NOT new at all. It was the cartridge originally designed by Browning when he was developing his rifles and machine guns. The military at that time decided it was not a "good" cartridge and made Browning re-design for .30 caliber.
The 6.8 is just another ploy to re-invent the wheel, as was the 5.56.
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