Two questions:

1) Have you noticed that the rear sight graduations are wrong? If it is dead on at 100 meters on the 100 meter setting, then it is low at 200 meters on the 200 meter setting. For 200 meters the 300 meter setting matches POI/POA. 

2) The rear sight leaf comes up during recoil. Every shot fired on the 300 meter setting moves the sight to the 400 meter setting. What's the solution to this? A new sight leaf? I have gunsmithing services I can use if it involves anything too serious.

ETA:  I am using 150 gr Prvi Partisan soft points.  

1 corrected I was thinking of the M91

2 check that the rear sight is properly installed. You can remove and reinstall it.

M38s are in meters not arshins...

If your ammo isn't what the sights were calibrated for then that is also your problem.

M38s should be calibrated for light ball...~149grn ammo.

Check the push buttons on the sides of the rear sight. They need to be in the full out position to lock the sight in place.