An adapter for coupling wellhead pressure control equipment to wellhead mounted equipment, includes a breech pin and a breech lock base assembly. The breech pin includes a tubular breech pin body and a rotating breech ring. The rotating breech ring is coupled to and rotatable relative to the breech pin body. The rotating breech ring includes a breech ring body and one or more breech pin teeth extending radially outward from the breech ring body. The breech lock base assembly includes a tubular base assembly body. An upper end of the bore of the base assembly body defines an upper receiver. The breech lock base assembly includes a fixed retaining ring including one or more fixed breech teeth. The fixed breech teeth extend radially inward into the upper receiver. The fixed breech teeth are positioned to correspond with the spaces between the breech pin teeth.