'Russian' Leather is a process, not a country of origin. Leather, specifically horsehide, was hand boned for several days to produce a leather with a very high surface silicate content. This leather was used for the highest quality razor strops. Today, 'Russian' Leather is machine made, but still at great expense, and only used in the very finest strops.
Horsehide is sold cut into specific parts, just as is cowhide. Cowhide is sold as 'backs,' 'shoulders,' 'double shoulders,' 'bends,' 'bellies,' etc. and a couple more. Horsehide is sold only as four cuts; 'shell,' 'strip,' 'single horsefront,' and 'double horsefront.' There is no real section of hide called horsebutt.
The 'shell' cut is the thickest, most uniform, and most dense area on the entire hide, and makes the very best stropping leather. The 'strip' is located adjacent to the 'shell' and is almost as good.
Please, if you are going to use horsehide as a strop, do NOT cover it up with compounds. The reason for using it is that horsehide has a much higher concentration of natural silicates, which are much finer than any compound we normally use. Vegetable tanned cowhide has these same natural silicates, but in a lower concentration.
Stitchawl