MOA stands for Minute Of Angle. A full circle
is divided into 360 degrees and each degree is divided into
60 minutes. Thus, there are 21,600 minutes in a full circle
(360 x 60 = 21,600). A minute is a small angle, but it's exactly
what's needed for gun sights. A rule of thumb is that changing
a sight's elevation setting by 1 minute of angle changes the
bullet's impact point by 1 inch at 100 yards. A more exact
value and how it's arrived at is shown below:
A circle with a 100 yard radius (distance from
the center to the edge) would have a circumference of approximately
628.32 yards or 22,619 inches (100 x 2 x pi = 628.32 {pi is
about 3.1416}). Dividing the circumference in inches by the
number of minutes in a full circle gives a value of about
1.047 inches (22619 / 21600 = 1.047). Thus, changing a sight's
elevation setting by 1 minute of angle changes the bullet's
impact point by 1.047 inches at 100 yards. And the bullet's
impact point would change by 2.094 inches at 200 yards (1.047
x 2) and change by 3.141 inches at 300 yards (1.047 x 3).
One so called "sight in" program makes the claim
that changing a sight setting by 1 MOA won't change the bullet's
impact point by the value predicted by the above paragraph,
which is 3.141 inches at 300 yards. A simple example may help
to show why this is in fact the correct answer. Normally there
is some random variation between shots, which will be ignored
in this example in order to keep things simple.
In this simplified example there is no need
to know the bullet's velocity, BC, or even the sight height.
All that needs to be known is that the gun is in a machine
rest and the bullet is striking 11.78 inches below the line
of sight at 300 yards. Also, assume that the same type bullet
is fired at the same velocity on each subsequent shot. Changing
the sight adjustment by 3.75 MOA (15 clicks at ¼ MOA per click)
would drop (drop is correct) the sight line by 11.78 inches
(3.75 x 3.141 = 11.78). Because the gun is in a machine rest,
the next shot's trajectory would be identical, but now the
bullet's impact point and the sight line exactly match at
300 yards.
So what happens if the sight line remains fixed
on a target, and instead, the gun's barrel is elevated by
3.75 MOA? This small change in elevation has no discernable
affect on the bullet's velocity or drop at 300 yards nor the
time of flight. Because of this, the bullet's impact point
would again coincide with the sight line at 300 yards; exactly
as predicted. The only way this could not be true is if miniscule
changes in the barrel's elevation caused significant changes
in bullet drop at 300 yards, in this case. Elevating a gun's
barrel is just like shooting up hill, and it takes a slope
of almost 2 degrees (120 MOA) to cause just a 0.015 inch change
in bullet drop at 300 yards, so a change of only 3.75 MOA
of elevation could not have any noticeable affect on bullet
drop.
The difference between most external ballistics
programs is not the underlying physics or math, which has
been researched and well understood for decades, it’s the
usability and interface features. In that arena we feel Ballistic
Explorer wins easily, and so do the many thousands
of shooters who have purchased our program.
