Most Mosins I've seen shoot high (Mine shot 8 inches high when set on the 100 yard or meter setting).
I have to keep mine "as issued" to be legal in CMP GSM (Vintage Military Rifle) Matches.
Windage is adjusted by moving the front sight which ever way it needs to go but if the rear sight is bottomed out, and still shoots high, then other means need to be attempted.
Playing with my slide rule I figured you need to move the rear sight up or down .0061 for every MOA you want to move it. As I said, my Mosin shoots 8 inches hight. So 8 X .0061 = .0488, would bring the sights down 8 inches at MOA.
I took the rear sight off the rifle (simple operation, just punch out the pin). I set the sight in the milling machine and milled .0488 off the bottom. Making no changes to the top part of the sight, there fore its still considered "as issued".
I put the sight back on the rifle and sure enough, the sucker is right on at 100 yards. I set the slider on the 200 mark, its on at 200, then at 300 its on at 300 yards.
The rifle now shoots like it needs to to be able to compete in GSM Games.
CPT USAR Ret
USAMU Sniper School Oct '78
Distinguished Rifle Badge 1071