This began life as a Martini Henry Mark IV military rifle chambered in the experimental .402 cartridge before being converted to the widely used .577/.450 Martini Henry cartridge. The gun shows all indications of long hard use in British India. At some point the rear ladder sight has been replaced and the rifle has been converted to smoothbore for Police use.
Attached to the stock is a brass plate reading "No.25 NIHALGANJ Police Dept" which may be connected to the 25 over DP stamped just above the brass plate. The Nihalganj Police Station still exists today within the Indian city of Dholpur. Several Martini rifles with similar markings have been found.
An internet thread discussing these interesting markings can be found at https://www.tapatalk.com/groups/britishmilitariaforums/markings-on-mk-iv-smoothbore-t15153.html