[Tailback]

we need to get rid of the 5.56 round and switch to a 6x45mm or 6.5mm
You're a man after my own heart! The 6mm or 6.5mm (.243 and .264 cal respectively) would be the perfect balance for an assault rifle. Add in the operating system of the German G-36, and keep the ergonomics and controls of the M16 lower reciever. That would be the perfect assault rifle and we keep the SAW and M-240 because there's simply nothing out there better than those two.

[Tailback]

Oops, to correct my post above the SAW would of course be switched to fire the new caliber.

[NY.SS-Bar9]

And don't forget the newly plentiful supply of once-fired brass and surplus ammo!

[yarddog]

I believe the perfect battle rifle cartridge was developed over 100 years ago. The 6.5 Swedish Mauser. There is a point where all the ballistic compromises meet. The 6.5 is powerful without excessive recoil.

I actually think the AR-15/.223 combo is about perfect for use against people.

I once fired a bullpup based on a Remington fireball action. There is something very unsettling about having that explosion going off right beside your face.