Quote Originally Posted by allmotoronly
It's actually the opposite. The larger round has a slightly lower velocity, which means there is less chance of a through and through. The knockdown power is almost three times that of the 5.56mm because this bullet has more of a tendancy to mushroom and cause maximum damage. The bullet also weighs about twice as much as 5.56 NATO rounds.

The 6.8 SPC was actually developed by request of some of the different special forces divisions who wanted something that could actually compete with the 7.62x39 found in the AK47. The different groups were pleased and some have adopted the round as standard (some navy seal divisions, etc). The only reason it hasn't been adopted by more of the armed forces is due to the price of retrofitting all of the current in service M16's and M4's.
is it just that round with the lower velocity? One of the reasons we went to the smaller round back in the 70's was to lower velocity of the 5.56. The 5.56 doesnt mushroom too much, what it does it bouce off of everything it hits and does alot of damage.
From a Corpsman friend of mine who did 3 tours in Iraq, that larger AK round probably saved at least 20 lives that he was part of when compared to a 5.56. They were through and through's that a smaller round would have caused much more damage.