Good question!!!!!
I do a fair amount of reloading for a Russian 7.62x54R MN1891/30 rifle.
7.62x54R and 7.62x53 R are the same. The Russians and most of the rest of the world calls it 7.62x54R, the Fins for some reason view it as 7.62x53R. Of course the Fins don't think that an 8mm Mauser should be called 8mm they call it a 7.xx mm. They seem to have a thing for their own measurement system.
I have reloaded Century Hot Shot, Graf & Sons, and Winchester Metric 7.62x54 R brass. I like the Winchester Metric best, but the Graf & Sons is fine brass and shoots very well.
Now to add more confusion, most of the surplus Russian rifles are designed to use .310 (not .308) diameter bullets. However, since most of the milsurp Russian rifles saw decades of heavy use, they tend to work best with either .311 or .312 diameter bullets. Typically these bullets are advertized as British .303 bullets or Japanese 7.7 mm bullets. (Go figure?)
There are a few bullet manufactures that make .310 bullets in heavy 147 to 180 grain bullets. There is also one manufacturer that makes a .3105 match bullet.
From what I have read, a few Finish MN's had some .308 barrels and there were some US made rifles made prior to WW1 that had .308 barrels and were designed for use with 7.62x54 R ammo. To further complicate reloading, if you buy a set of Lee 7.62x54R reloading dies, they will give you a neck expander built into the sizing/deprimer die that is just a .308 diameter gizmo. That can create lots of headaches when you try to load .310 or .311 bullets. As such you will either need to grab the neck expander from a .303 die or a 7.62x39 die to do your MN reloading.
Of course if you start loading cast bullets for your mil-surp Russian rifle, you probably want to use a Lee .313 sizing die and either .313 or .314 cast lead bullets. But hey, they never said that life would make sense.
