jonnyjet

I like the looks of the salt works, but they only make a DPMS low, and do not plan on making a high. (I already have my rail)

Hotrod is correct on the matrix using a Armalite barrel nut. Here is my Matrix with a 16 inch barrel.

I am building something very similar. I had it all together with a Matrix aerospace receiver, but it was too sloppy, I am going to switch out and get a mega. For the gas block if you have not looked at the SLR rifleworks they make a great adjustable gas block.

I had an issue like this, the bolt catch was stopped by the upper receiver before it would fully hold the bolt. I had to remove the bolt catch, trim it a little with a dremel and it works fine now.