This thread will try to show just how easy it can be to build your own upper. Just like doing your own lower, the key is to do your homework before you start ordering parts. Selecting the right parts to compliment each other is even more important on the upper, as many combinations of parts just won't work together. For me, the only real concern I had before starting this build was with the gas block. Getting it aligned and secured properly had me a little worried. I was just minutes from pulling the trigger on ordering a stripped Daniel Defense barrel and a low profile gas block from Midway, when I saw this barrel on AIM Surplus: It was cheaper that the same barrel from Midway (with the arfcom discount code at AIM) and it had the FSB already pinned, but not locked down. Saved me about $20 on the barrel and $25 by not needing a gas block, plus it solved my dilemma. So I ordered the barrel assy. and complete DD BCG from AIM. I also ended up ordering the gas tube from AIM, after I goofed and ordered a rifle length tube from Midway. The DD upper receiver, Troy rail, BCM charging handle, Magpul sights, and Magpul AFG2 all came from Midway.