Here is one of our favorite custom builds. We decided to try and rebuild the old school USAF 604. These are using a true 20" .625 pencil barrel with a 1/12 twist. The barrel is made of 41V50 steel and the chamber/bore is chrome lined. We have also used a A1 Bird cage flash hider on it. Upper receiver is black finished. Handguards are our new production. BCG and Charging handle are not included.
Take a look at this great article about our upper http://www.gunsandgunsmiths.com/retro-ar-project/