During the Spanish Civil War the Soviet Union supplied arms, including M91/30s, to the Republican forces. These were exported to the US in the 1960s and were some of the first Mosins seen by US collectors. Condition varies greatly and similar to Finland they can have a mix of parts including incorrect front sights. Many were marked "MADE IN USSR", or oddly "MADE IN URRS", by the importer and this is a dead giveaway of Spanish origin as no other imports were marked in this way. The Spanish MP8/flaming bomb mark is another identifier. Less common even than Finnish marked Soviet M91/30s, Spanish M91/30s are an interesting part of any Mosin collection.
WW1 or WW2 meaning M91, 91/30's, dragoons and possible cossack rifles were used in SCW. There are many factors, like replacement handguards and cleaning rods, but the mosr obvious indicator is "USSR" stamped on receiver.
Here is a great website containg info on mosin nagants
Don't forget the wire sling hangers (front wire hanger is usually missing because they're very brittle with age, and taking off the rear barrel band is impossible without removing the forward hanger, so when inexperienced folks try to take them off, they generally snap in half) and lack of standard import marks.
Here's a 1934 91/30. No import marks. No made in USSR. Total mixmaster. Wire sling hangers. Beat up stock. Metal and bore in great condition. Finish looks almost identical to the finish on my FR7 and FR8. Plus, a neat little repair to the stock on the right of the receiver. Is it SCW? I think it is.