Those crazy Canukians!
The upper is aluminum and anodized and has a large diameter thread. To get the threads to seat to each other correctly, torque it three times using some kind of assembly lube. Otherwise, there may be tight spots and loose spots. Evenly loaded threads will keep from loosening up better and won't need so much torque.
Blessed mother of all kittens. Torquing the barrel nut is very simple, yet people make it more complicated than landing a rover on Mars.
Rather amusing, actually

