I found a Mosin Nagant this past Tuesday in a local shop. It was Finnish made in 1917 (hex receiver) and later captured by the Russians as they stamped a hammer and sickle on the receiver. It's in nice shape and all the parts match except it has a Russian trigger housing. The owner of the shop had no idea what it was and I wasn't going to do his research for him. I got it for a very reasonable price.
I'd like to see pictures of that over on the "Other makers" forum.
Edited to add comments after more research:
First off, the Finns did not manufacture your 1917 marked rifle. All Mosins of that period were produced in Imperial Russia or the US and marked with the Russian imperial Eagle, either on the receiver or the barrel shank. All "Finned" Mosins were taken from the Russians during the Finnish War of Independence, the Winter War, or the Continuation War. That many were rebuilt into distinct Finnish models is another story, but all the receivers were taken from Russians at some point.
Hammer and sickle stamps on the receiver are usually placed to deface the imperial eagle mark some Mosins have on the receiver. As far as the collector community can tell, this was done when the Soviet Union was created.
Finnish capture guns can only be positively ID'd by the presence of one or more of the following stamps on the barrel shank: SA in a box, 41, or a D to indicate the throat is reamed for the Finnish D166 round.
Finnish guns recaptured by the Soviets are a bit more difficult to nail down, but the following features are pretty indicative.
1) The barrel shank is SA marked, but the stock is clearly a shellacked Russian refurb.
2) The barrel shank and sometimes the stock carry a refurb facility mark. The square with a diagonal line (AKA "Diver Down") mark is the most common, from the Balakliya facility in Ukraine.
3) Any Finnish stamps on the barrel shank have been struck through
4) The import mark near the muzzle says Russia.
