This is a later pattern Viewer, introduced in 1893, the EFD marks are post 1897.
This pattern was designed for the inspection on .45" Machine Guns, and "Martini Henry Rifles in Naval Service", land service used a small polished plate, in the shape of the breech block to reflect light. In the Mk1 service rifle from 11-1874 until 8-1877, the block on the Martini was polished bright, to do exactly the same job. The men complained it was a job to keep corrosion free, so, under LOC the were "Browned", or Blued.
This is a .303" calibre, although drawings exist of an earlier pattern in .45", but this does not have the folding handle so incorrect for anything but .303" and late service .45 weapons.