Here is one of our favorite custom builds. We decided to try and rebuild the old school M-16A1. These are using .625 Government barrel with a 1/7 twist. The pencil barrel is made of 416SS steel with a 5R polygonal bore, and the barrel has a melonite QPQ finish inside and out.  Upper receiver is black Type 3 hardcoat anodized. Handguards are our new reproduction.

Specs:

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

Barrel: TNTE Pencil 20" 1/7 5.56 NATO Polygonal rifled 5R with 1/2x28 thread with M4 Ramps

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