Well, as I said before the XM-29 is -probably- going to be scrapped. And then will instead be replaced by better production numbers/deployment numbers in the XM-8 and XM-25. Which are practically what the XM-29 is, but just instead of both .223 and the smart 25mm both being in the same weapon, they will be separate systems. And, uh the XM-8 can come in a whole variety of barrel lengths, and calibers, if desired.
As for your other statement, I suppose you would be reffering to the XM-307/312. It is a two man crew served weapon, which is the most capable, technologically advanced, deadliest, multi faceted, and lightest crew served weapon that has ever been designed. Available in both 25mm and .50 cal it is the most likely candidate to replace the aging Browning .50 cals and HK Mk19 40mm grenade launchers.
To answer your Q really the only place for these CSW's on the battlefield are mounted on MBT's and APC/IFV's or other vehicles, other than that they are more than likely going to be defending fixed positions. Even though the weapon only consists of 2 parts, and only weighs in at 22.7 kg.
Don't know what that equals out to in pounds but it sounds pretty light