"3. Four shots are fired. They must hit in a box 15cm (I'll have to check that number) above the point of aim. That's about 6 inches. Group size needs to be about 15cm as well; again, check this or I'll have to find time to do so.
This should roughly equal point of aim at both 100 and 200 meters, but might still be a little high. Not a foot, though!"
Might double check on the ammunition used for "zeroing". Most "D" ammunition I've tested in M91/28s will hit about 6" high if the sights have not been changed. That is right at a 300 meter zero with that ammunition. The lighter weight and higher velocity of "L" ammunition does make it hit higher, about 8 - 10" at 100 yards/meters. If "L" ammunition is used then the rifle must be zeroed for that ammunition. With original M91/28 or earlier sights that were in arshins they are actually zeroed (if correct) at 400 arshins; about 330 meters. Thus they will hit even higher with "L" type ammunition.
M91/30 sights are different having shorter range sight setting allowing for the zeroing procedure you mention. No way of knowing with milsurp rifles if they were correctly zeroed and what ammunition they may have been zeroed with. It's a **** shoot.
Larry Gibson