In reviewing photos of the Parkhurst - Warren device in "The Krag Rifle Story", page 79, it appears Mallory and Olson used a photo of the Model 1892 'test rifle', as well as, two photos of a Model 1898 action bearing the device.  Model 1892 rifle #4070 was the Ordnance Dept. test rifle and was in the Smithsonian Institution, when Mallory Published (1979).
  d rail's photos of his device show a strong resemblance to the device on the Model 1892 in the photograph used by Mallory.  (IMHO)