Sep 21, 2020 · Check out our favorite picks in Best .300 Blackout Uppers. And of the newest flavors of this year is the .224 Valkyrie which slings ~90 gr bullets up to 1300 yards…in an AR-15 lower platform! PSA .224 Valkyrie At High Bar Homestead Product Details: AR15 Complete Upper Assembly – 7.5 Inch / 300 AAC / Side Charge / Keymod / 160023 Pistol Length Gas Tube. An essential component to your AR15 is the gas tube, which keeps your build up and running. This gas pistol-length tube is constructed from corrosion resistant stainless steel ensuring a lifetime of service.