Just picked up a complete FN M16A2 upper to use as NRA across the course rifle. Are the FN barrels as good as the Colts?
yep!
btw…without pics you have nothing. 
It should work just fine. Where are the pics?
PICS!!!
It seems that Colt - Connecticut barrels are button rifled while FN barrels are hammer forged. Plus Colt has not always had perfect QC. So you probably did better with the FN upper.
Let’s see it!
FN M16 barrels are not hammer forged.