As a huge KX3 fan please let us know how the kak compares...I have been planning a 'lightweight' build...and it would be in my plans if it is all decent.
Here's the 3 for 1 deal...
http://www.kakindustry.com/ar-15-parts/upper-parts/kak-industry-slim-flash-can
There is a lot of weight in that rifle that could be saved.
Eventually I plan on applying for my tax stamp to make it a sbr.