Nice review.
A few questions:
What are the other main components made from i.e. receiver, top cover, feed tray, barrel, bipod etc - steel, ally?
Does the gearbox use ballrace bearings and what diameter are they? It would appear that the Sector gear has, at least, ballraces.
Do you know if the hop unit is compatible with other makes i.e. replace it entirely?
Cheers.