Has anyone seen this new Sig516 Upper Receiver Kit for the AR? I got this in an email from Sig Sauer today. They say that sales are limited to 300 units. Went to their web page but couldn't find it anywhere. Which is why I am asking you all. I guess I wanted to see what you all thought of it. I knew that they were selling the Sig516 as a complete unit, but apparently you can buy just the upper now.