The OICW got put on hold because of weight?
Gee, we have an opportunity to increase the firepower available to an infantryman by 1000% but it's a little heavier than a M16 so screw it...
It was more than a little weight.
Some quotes from answers.com (not always correct but most of the time close)
"The final prototypes of the XM29 weighed in at about five and a half kilograms when empty, and nearly seven when loaded. Soldiers also complained of the sheer bulk of the weapon system."
Thats 12lbs unloaded and 15lbs loaded. Thats a tad heavy in my mind.
Also LOOK AT THE SIZE, how are you going to haul THAT around. And forget about using it in a Humvee.