Take this for what its worth.
I live about an hour from the Core 15 HQ in Ocala. I decided to build one and have purchased the upper, lower and parts kits from them. Sure, I could have found a better deal on the internet, but I wanted to pick it up in person. The fit between the upper and lower is perfect, no slop at all, not that that means all that much.
But the thing that impressed me is the customer service. The trigger guard was missing from my parts kit, I called and they sent me their upgraded trigger guard by noon the next day.
This post was edited on 11/14 at 7:43 am