As already pointed out, the .455 S&W
Second Model (not Mk-II) Hand Ejector revolver was never Mounted Police issue - rather, they began replacing their .476 Enfield revolvers (in service since the early 1880's) with the Colt New Service revolver, chambered in .455, around 1904. Canada had acquired about 1000 Colt New Service revolvers - chambered in .45 Colt - around 1900, for military use during the Boer War - but the RNWMP Colt revolvers were .455 caliber. Following formation of the RCMP in the 1920s, by amalgamation of the RNWMP with the Dominion Police, the Force also purchased that same model in .45 Colt. However, to minimize ammunition supply problems, the .455 version was kept as standard issue in the western Provinces and Territories and the .45's were issued to personnel in Ontario and further east.
However, this model of S&W revolver
was Canada's primary military handgun during World War I - about 14,500 of them were acquired in 1915 and 1916 (in addition to 5000 .45ACP M1911 colt pistols in 1914.) Does your revolver have any Canadian government markings, such as the C-broadarrow? Not that absence of such markings is a problem - pistols were primarily an officer's weapon, and officers were then required to supply all of their own kit, including weapons, at their own expense. Thus, the majority of the pistols acquired by the Government in WWI were resold to officers, and did not have any such Government ownership marks applied, as those marks would then just have had to be "cancelled".
My own S&W 2nd Mod. Hand Ejector (also sometimes referred to as the "New Century" model) is one example - it bears no Canadian Govt. markings, but I have a provenance letter from the S&W Historian confirming that it was shipped on December 24, 1915 to "Canadian Government, Ottawa, Canada".
For more information about 20th Century Canadian military handguns, you may find this online photo essay (... authored by "yours truly"...
) of some interest:
http://www.canadiansoldiers.com/weapons/pistols.htm
