Here is one of our favorite custom builds. We decided to try and rebuild the old school M-16A1. These are using .625 Faxon Gunner barrel with a 1/8 twist. The pencil barrel is made of 41V50 steel, and the barrel is QPQ.  Upper receiver is black finished. Handguards are our new reproduction.

Specs:

Upper: TNTE CH Marked A1, Black Type 3 hard Coat with DFL

Barrel: Faxon Guner 20" 1/8 5.56 NATO with 1/2x28 thread with M4 Ramps with tapered delta ring

Gas System: Rifle

Gas Block: Pinned on A2 Standard FSB

Handguard: Two Piece Drop In Triangle (NEW)

Flash Hider: A2 (other options available)

BCG: Mil-Spec

Charging Handle: Mil-Spec