Well, this rifle [FNH MK16CQC
] is a recently manufactured select fire weapon. The sad fact is US Civilians living in the US are not allowed to own any select fire weapon manufactured after May 1986. The Hughes amendment to the FOPA '86 prevents you from personally owning one.
You would have to commit a felony to own one. (10 years AND $250K max, I think)
EDIT: Well that's not strictly true. You could become a Special Occupational Taxpayer (SOT)
and sell them. That would allow you to possess for the purpose of selling them to LE/Mil.
You can own the MK16S semi-auto version of this rifle. I'm not sure if a short "CQC" barrel is available, but if it is you could register this as a Short Barreled Rifle (SBR) under NFA '34 and own it legally.