I assembled a 16" Criterion .308 using an Aero Precision upper, lower and hand guard. Went together easily, just like a big ar15...
Looking at either the Vortex PST Gen II 1-6x, mrad or the Athlon 1-6x Midas BTR, mil reticle. I was able to see and handle the Vortex but any Athlon is rare...