The NBS Slick Side Billet Upper Receiver is a quality, American made billet upper featuring a unique design that sets it apart from traditional forged upper receivers. Manufactured to exacting standards on five axis CNC machines from a solid block of aircraft grade aluminum, this stripped upper not only looks good... it is built to last. M4 Feedramps Compatible with mil-spec forged lower receivers and most billet lower receivers .250 takedown / pivot pin holes No forward assist Designed to be used with or without a port door / dust cover (will need to remove e-clip from dust cover pin before assembly) Weight: 7.1oz Made in the USA Backed by the NBS Limited Lifetime Warranty