I've got an Anderson lower in my sock drawer and it is slated to become a .300 BLK pistol. 10.5 inch upper is what I'm going with.
I would like to do the same but until I build one I don't feel comfortable buying in bulk, especially for a new on the market lower. I bought a couple AR57 brand lowers, really liked the way they looked, but when I built the lower I ran into a couple issues, the main one being that the safety lever would not rotate completely up. It was just a few degrees off and didn't effect the function of the lower, is was purely cosmetic, but it bugged me enough that I sold the lowers.I'm gonna get a few of those (Anderson lowers) and just put 'em up.