Upgrade your standard top cocking upper receiver with this side cocking upper receiver. It comes with a 9mm barrel and steel military spec picatinny rail. The rail height is available in two heights: 1/2″ (standard) and 1/4″. The rail height shown is 1/4″ and there is an additional $25 fee due to the customization of the rail height. There may be a slight delay on the shipment of this product due to the custom picatinny rail height.