This is a Luth-AR Upper known as the 24" Bull Barrel Complete Upper chambered in 223 Remington, model FTBL-B24.
The Luth-AR 24" Fluted Bull Barrel Complete Upper Barrel Assembly Starts with a 24"" .223 caliber fluted bull barrel made from 416 SST with a 1-9" twist mated to a A3 Flattop receiver which includes a bolt carrier" charging handle" forward assist and ejection port cover. The upper is then topped off with a lo-profile gas system and an ergonomic 15" Palm Handguard(R) with KeyMod slots and a Picatinny top-rail.
Features:
HG-V-15K – Palm Handguard® – Vented 15″ KeyMod with Barrel Nut
BL-B24FT – 24″ Bull Barrel, Fluted, Threaded 416 SST
FTT-EA1 – A3 Upper Receiver Assembled
BC-A-223 – Fully Assembled Bolt Carrier – .223
UR-19 — Charging Handle