There was an AR-14, or at least a design for one. https://www.forgottenweapons.com/yes-the-ar-14-is-a-real-gun-sort-of/ The guy who made this video seems to know his stuff. Look up “Forgotten Weapons” on you tube.
I regularly follow Ian on ewetewb ... I agree that he knows his stuff. His video on the topic suggests that Armalite never actually made an AR14, though drawings and a patent do exist.