Umbrella Corporation's latest forged upper receivers are manufactured to military contract specification. They feature machined M4 feedramps and come fully assembled with round forward assist and port door/dust cover installed. And they intentionally leave off the traditional "T" markings on top of the Picatinny rail so they better match unmarked handguard assemblies (KAC, Vltor, etc.) and likewise prevent mismatched engraving styles. Their deep laser engraved logo on top of the rail marks these as an Umbrella Corporation product. As with all of their parts, they carry an unconditional guarantee against material defect and manufacturing failure.
Barrel assembly should be performed by a qualified Armorer: Mil-Spec AeroShell 33MS barrel nut grease is included.