Thanks--it's actually pretty basic with mostly budget parts--except for where it counts. Cavity back sells the magazines--though you can cut out your own but have to be careful to use a strong enough magazine with uniform front (no riveted lap seam as many are) and also that it doesn't swell side-to-side under pressure of the cartridges. I've used some top brand magazines that still had follower tilt issues--and that can create feed problems. I built an AR 10 chambered in 284 win and had to make my own open-front magazine, but it swells a bit too much after 5 cartridges are inserted. Just noticed they are out of stock--which happens a lot--they used to allow back-order (which is what I did) you may want to call and ask, I forget the guy's name off the top of my head but he's a really nice guy and works closely with Harrison of ARP barrels.