I have a 1970 unissued m39 I took shooting for the first time today. It was very consistent but was shooting pretty dang high, at 50 yards I would aim at the bottom of that target and hit the bullseye and at 100 I had to aim way down. I know they zero these things at around 150 meters but that shouldn't account for such a difference. Anyone have an idea what I can do to rectify this? Buy a shim set? I am going to scope it some day but want to have it reasonably zeroed with irons. Thanks.