Another Jeffery rifle with such a "musket stock" is shown in this picture, though it is not a Mannlicher M92, but a Mannlicher – Schoenauer M1900 in 6.5x54 M-S.

The rifle is obviously mounted with Jeffery's early idea of scope and mount.

This was the favorite rifle of Major Percy Horace Gordon Powell-Cotton (1866 – 1940) https://en.wikipedia.org/wiki/Percy_Powell-Cotton .
Later, he had the foreend shortened to "normal" rifle half stock length. Some years ago I saw that rifle at the Powell-Cotton Museum, Quex Park, Kent. The museum is the giant "Trophy Rooms" of the great hunter and explorer, a "must see" for anyone visiting southeast England.
http://www.quexpark.co.uk/museum/

BTW, Westley Richards offered a similar stock configuration with 21" barrel in their 1912 catalog: