New upper or kit

[Whelenon]

http://jtdistributing.net/store/product1280.html
http://www.kiesfirearms.com/Home_Page.html
http://www.bravocompanyusa.com/Vltor-VIS...length.htm
http://www.lokiweaponsystems.com/products/
http://www.blackholeweaponry.com/catalog...a8b93fc924
http://www.jprifles.com/
http://www.lesbaer.com/264LBCAR.html
http://templarcustom.com/templarconsulti...ifles.html
http://www.precisionfirearms.com/
http://www.alexanderarms.com/

Here's some that I've found on-line, start with Alexander Arms, they developed the Grendel and is the benchmark.
Welcome to the board.