Looking to go a different route. Colt M4 HBAR 16-inch upper topped with an Aimpoint RDS. Upper is ZEROd via red dot and co-witnessed with the iron sights. This upper has no recoil.
Things added: Magpul rear MBUS gen 3, BCM extended charging handle, BCM BCG (will come with the original Colt BCG), Q-cherry bomb compensator (I do not have the original A2 flash hider anymore). I also put some shock cord around the hand guard as a sling retention band.
The Aimpoint RDS will also come with an Arisaka offset mount as well as a Holosun low mount. All in all there is about $1,700 if you piece everything out. Looking for $900 all together or a trade for a 18-20 inch AR15 upper.