Quoted:
Here's my experience with Mosins. I own 3. An ex-sniper 91/30 straight bolt, hex receiver, 1934 date stamp. 1944 M44 round receiver, 1938 91/30 round receiver. The ex-sniper shoots about 1 foot low at 50 yards. The M44 shoots about 1 inch low and 4 inches to the left (with the bayo out), so kentucky windage comes into play. The same is true for the regular 91/30. In all honesty, Mosins are kind of hit or miss for me. man sized targets are do-able at 100yds but don't expect any real accuracy. You can adjust the sites and get lower or higher front sight posts, I have too many toys to shoot to really worry about a high standard for Mosins. Get a Finn if possible, if you want something cooler get a K31 swiss, it's the most accurate open sights C&R rifle I have. YMMV, thats just my $.02.
Not trying to be argumentative, but only to find what the issue might be.
If you're shooting a foot low at 50 yards, there's something very wrong. For the others, you can adjust the sights very easily. You can't really blame a gun for being inaccurate if you haven't zeroed it. Also, the key is finding what ammo the gun likes and they're all different. Personally, I think that if the gun isn't shooting groups less than four inches (and that's bad) at 100 yards, there's something wrong with the equation. I own/have owned nearly fifty of them and have found that most will easily shoot in the 2-3 inch range, with the right ammo, if I do my part. Quite a few of those would do half that. You should be able to hit a clay pigeon at 100 yards, with relative ease. It may require some minor hold over/under, but should be consistent.