A blowout preventer comprising: a main body comprising a seal seating profile, one or more bonnet guideways, and one or more slide guideways; a bonnet attached to the main body, wherein the bonnet comprises one or more guide rods, a ram unit, and a seal seating profile; two retention units attached to the main body and the bonnet, wherein each retention unit comprise a clamp block, one or more guide rods, and a bonnet guideway; and a metal seal, wherein the metal seal is seated in the seal seating profile of the main body and the seal seating profile of the bonnet.