I think you have confused accuracy with ....??? Accuracy of a
weapon refers to how consistently the round behaves after it leaves
the barrel. So If i fire, and the round hits above the target, in a
perfectly accurate weapon, if i aim at the same point and all else
being equal, the round will hit at the same place.
eg. At 100m
I expect an M16 to be very accurate. If I aim at the chest of fig
11, and the round hits the head, then because the M16 is accurate,
I know that if i aim at the chest again, the round will hit the
head.
A revolver on the other hand is not as accurate as a rifle. At
100+m if i aim at the same point, I can expect there to be a
variation as to where the round falls due. If i aim at the chest,
at the round hits the leg, the next time round i fire may hit the
ground, etc.
Zeroing is so that the round will fall where you aim at. It has
nothing to do with the accuracy of the weapon. Maybe we can say
that zeroing improves the accuracy of the firer since he does not
have to offset his aim point. It improves his accuracy because he
does not have to estimate where to aim. Rear sight, front sight,
Boom! No need to aim left, or up or down. His inherent marksmenship
ability is not improved simply because he has zeroed his
weapon.