Russian M1895:
The Nagants were popular with the Russion Army, as they had so-operated in the development of the M1891 (Mosin-Nagant service rifle) The Russians adopted the 7 shot solid framed Nagant gas-seal revolver in 1895. The earliest double-action guns wre purchased from the L. Nagan & Cie, Liege. The first guns seem to have been issued to officers and senior NCos. Production began in the Tula Factory in 1899, whereupon assembly in Belgium ceased.
Guns made in Russia prior to the 1917 revolution were almost all single-action, and these were issued much more widely than the original Belgian made batches, and have come to be known as "the Troopers Model." Production continued in the USSR until 1945.
As Jim mentioned they were strong, reliable and easily maintained. This is expressed by an ex-Tsarist soldier who once replied: "if anything went wrong with it you could mend it with a hammer."
The 7.62mm caliber of the M1895 allowed Russian barrel making machinery to be adapted for service for rifles or revolvers with releative ease. The stopping power of the bullet was not great, though a slight improvement was obtained by flattening its tip.
HJN