I don't know of a site or book with the values for each different arsanal and year but they seem to be all pretty much the same except for the Fin ones and some of the really old ones. If you want the best out there buy a Finn M38 or w/e but be prepared to pay a little more. Best thing to do is just look for one with a good bore and no rust or pitting (check under the wood too if you can you only need to take off 2 clips and 2 screws) if all the metal work looks good, buy it.
The worst that's going to happen is that you get one with an oversize bore and it won't shoot that well in which case sell it, buy another one and you've only lost about $25.
From what i've seen ammo prices tend to vary a great deal, best thing to do is look around and when you find some cheap stuff, look on here http://7.62x54r.net/MosinID/MosinAmmo.htm and here http://www.surplusrifle.com/ to see if it's any good and if it is buy all you can because it isn't getting any cheaper.
Stay away from Albanian stuff!
While on the topic of MN's has anyone tried bluing the bolt? Or have pics of what it looks like? I've noticed my bolt is always the first place rust appears (Especially around the handle) and it's pissing me off, i'm thinking of bluing it but don't want to if it will look shit

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