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.