Clearly I need to shoot it more so I can give it a better report, but like the title says... I'm phoning it in today.
* I shall try to explain.
Because a scope is mounted above a rifle's barrel, the focal point must be adjusted downward so that it intersects the path of the bullet. This means that when you are looking through your scope at a target in front of you, your rifle's barrel is actually pointing slightly upwards, so your bullets will arc upwards for a bit until gravity and air friction slow it enough that it starts to come down.
Interestingly enough, all bullets do this, so the thing about ballistics is finding the points where the rising equals the falling. If you do that, then you can zero your scope at the shorter range where it's easier to see the grouping and know that you're good to a further distance.
So looking at the Mosin-Nagant round, you see that it intersects at both 25 yards and 200 yards, so if you zero a Mosin at 25 you're good at 200. Based on some vaguely-recalled calculations from other people, 2" high at 200 ought to be dead-on at 300.
Why 300? I dunno. Maybe I'm just feeling badass.