From my under standing the 6.8 is just to be isued to spical forces.
but the armey is looking at up grading the 5.56.
from some of my books theas are some posibiltys 5.56 with heaver bullets the 77gr is all ready in use by some units. but they are looking at the posibilty of going up to 100gr.
a 6mmx56 a new disined 6.5 and 30 cal.

they all have inhansed capibiltys but as a stop gap the 5.56 in a heaver gr or the 6x56 would be the cheapes option by far.
with juts a riffling rate change with the heaver bullits and a barral change with the 6.56.

as a side note the 6.8mm is verry close to what the brits wonted to use when we talked them in to going with the 308. i think it was called 270 ross or some thing like that.

the army does use ammo that is not fmj btw the mach king hp are used in sniping.

but the maine disine of the bullet is not to expend evan thought it does.

the yaw in some fmj do actualy brake up in to fragments but does not tencanly 'expand."
or at least its not the primary fuction of the bullet.

some of our aversary or past aversarys used hollow cavateys in the fmj to ficilate brake up and yaw.

from my reading on the subject and from test the "cert" team did i have come up with the conclusion that the lighter 55 gr fmj when they were barraly stablised by the riffling in early test proved to be more conducive to brake up and more boady dammage.

but the new twest rates are have some bad efects with stoping power "brake up"

the newer heavy loads for the 5.56 are more accert and have better pineration. but they are a little lacking in the yaw reducing the brake up efect.

with out the yaw you need weight and dimater to stop some one.