I have a DPMS lower parts kit, and have had it for awhile. I already have most of the parts I need in a pinch. But I like having those as emergency spare parts. As far as lower kits, so far they are available if you look, and not bad prices either. I hesitate to get new DPMS parts since I believe they are still being made overseas. The kit I have, was purchased before that development. I was thinking hard about a Stag Arms lower kit. Problem is, since I'm upgrading many of the parts a full kit is way overkill. Then again a full kit is less expensive then purchasing separately, and I would have MORE spare parts. I think all I really need is the take down pins and the magazine release. The trigger I'm putting in is a drop in. What am I forgetting? The selector spring? What is the spring that is exposed when you take off the castle nut?