I have a complete mil-spec lower that just sitting around doing nothing. I was wanting to know if anyone has used a Surplus Ammo & Arms upper. This is the one I looked at in the shop. http://www.surplusammo.com/surplus-ammo-arms-complete-ar-15-m4-16-upper-receiver-5-56-1-9/ Full upper 1/9 Chromoly 16".