6mm, just reading back through some posts, and a thought on your gas block pic rail. My RRA Coyote has a gas block with pic rail, however, really designed for a front sight post to mounted if needed. Be careful mounting offsets and lots of weight, it may affect your POI and such with the barrel harmonics. Just a thought. Keep us posted on your progress with the new scope. Can't wait for pics!!! I'm still toying around with the Xsight idea as well, so reading with interest!!
