.280 Enfield...Ahead of its time

[stanc]

...it isn't the choice of parent cases which is the constraint on cartridge design, it's the maximum permissible overall length for the round to fit within an AR-15 action.

Why should that be a limiting factor?

Paul's MRMG concept requires a cartridge solely for the infantry machine gun, not carbines or rifles.

And in the event the military should want a universal cartridge, they could develop new rifles with longer mag wells.