So I'm building my first pistol in 6.8. So for my thoughts on parts so far are
-Zombie defence lower with (pistol 6.8) engraved-on its way! After 10 week wait! do to lower milling machines down
-M4 flat top
-Spike's lower enhanced lower parts
-Noveske stainless 8.5" barrel
-Thinking of a Adams arms pistol piston system
-Like to get spike's tac.9" bar rail but I'm not sure if it'll fit with piston system  
So that's what I have so far a big question I have are I don't really like how the buffer tube set up looks and a see companies put out pistols with out them like rock river,Sig-sauer. So what reliable options do I have?
I really like the spike 9" bar so if you've seen a 6.8 low profile piston system for  8.5" pistol barrel post a link . I've seen system that go right in gas block but I don't know how reliable or adjustable they are.
Let me know what you think love to hear your input on this build.

I got the older adams arms pistol piston kit and it runs great on my 7.5 inch 6.8 upper.