This Matador Arms MAT-9 Roller Delayed Bufferless Upper Receiver Assembly is side charging, non reciprocating and features Matador Arms patent-pending EZTS "Easy Take-down System" with no tools required to break down the upper for maintenance and cleaning. The 9mm upper is machined for maximum weight reduction, slim profile, and compatibility with bolt catches and lower receivers. The upper is also built with a tapered multi-material 4-piece trunnion system to maintain mechanical accuracy and durability.The MAT-9 9mm AR upper is compatible with AR-9 Lower receivers in any double-stack magazine configuration:GlockSig SauerColt Stick MagazinesHK MP5CZ Evo Scorpion FeaturesNon-reciprocating steel charging handle (ambidexterous)4140 Nitrided steel bolt and action parts6061-T6 anodized upper receiver4150 Lightweight Nitrided Barrel, 7.825" long, 1:10 twist, 1/2x28 threadsNATO 1913 Spec top rail3 MLOK slots (both sides, bottom)Compatible with LRBHO (Last Round Bolt Hold Open) lower receiv...