The XM8 isn't the US's new assault rifle. It's pretty much dead and not going anywhere.
Dead? Last I heard that it was going into full use by early 2006.
Brig. Gen. Benjamin Freakley, "Another benefit to the local economy could come in the next few years to the businesses involved with the fielding of the XM8 rifle. Currently being tested by an “experimental force” of about 150 Soldiers from 29th Infantry Regiment, Freakley said that, despite errant reports, the XM8’s possibilities look promising.
“We just completed a proponent assessment of the XM8 rifle. It was reported that the XM8 rifle was cancelled — that’s not fact,” he said. “The money exists in the XM8 program to continue to experiment with the XM8 rifle.”
During the next year or so, Freakley said, the unit will continue to refine the rifle to “exactly what Soldiers need.” And if all goes well, several brigades in the Army will one day be issued that rifle.
“We’re optimistic about the rifle,” he said, “and the money stands behind the rifle to continue experimental development. And the money could be placed behind it to go ahead and purchase that rifle, which is good news for Columbus and the companies involved in that.”
The XM8 isn't going anywhere because the X represents experimental. The M8 as has been reported in the shooting press is a 6.8mm, .270 caliber Remington.
From what I have read it is a go with the Army and is being used by some Spec Ops personal in Iraq and Afghanistan.