Like some others already pointed out, be aware of the barrel dimensions at the throat and the muzzle. Many Mosins are cursed with sewer pipes for barrels due to the only ammo available being corrosive. Check the bore for pitting and the like before purchase. Even if you get one with a nasty bore, it will still be a fun gun to shoot for a relatively low price compared to more conventional chamberings like .308, 30-06, and .223. Make sure you find one with a decent barrel and you should be set. ALWAYS clean the rifle directly after shooting to keep it from being attacked by corrosion.
I put 80 rounds through it on Saturday. The one I got is from 1927, which means it's either an ex-dragoon or a prototype 91/30. The barrel was in outstanding shape. I live in Illinois so there aren't that many ranges around, the only one that allows rifles is only 50 ft, but I could tell it was in good shape... it shot nice groups.
You guys weren't lying about the recoil, my shoulder has some bruising on it, but it wasn't that bad. These things certainly weren't made for comfort. I don't have any clips so I loaded each round individually and burned my thumb on the metal every time I put one in.
When I was done I Windex'd the bolt and barrel, went home, poured some hot water mixed with dish cleaning fluid through the barrel, on the metal, and on the disassembled bolt, then cleaned like I normally would with some special attention given to the barrel.
This rifle is definitely a good deal, so is the ammo. I wouldn't want to be on the receiving side of a Mosin.