**[Common Lisp][1], 170 bytes**

    (let ((r "ABCDEFGHIJKLMNOPQRSTUVWXYZ"))(loop for i from 1 to 51 do(let ((l (subseq r 0 (- i (* 2 (- i 26) (floor i 26))))))(format t "~a~a~%" l (subseq (reverse l) 1)))))

Formatted:

    (let ((r "ABCDEFGHIJKLMNOPQRSTUVWXYZ"))
      (loop for i from 1 to 51
        do(let ((l (subseq r 0 (- i (* 2 (- i 26) (floor i 26))))))
          (format t "~a~a~%" l (subseq (reverse l) 1)))))


  [1]: https://rextester.com/QUCIAZ36175