**3.4
Trajectory Considerations for Sighting in a Gun**
The terms “sighting in,” “zeroing
in,” or “zeroing” a gun all mean the same thing:
adjusting the sights on a gun so that it shoots to point of aim
at a selected range distance. Sighting in a gun always takes place
on a target range, which may be an informal range in the countryside
or an established range in some convenient location. The procedure
for sighting in is familiar to almost all shooters. However, three
questions arise frequently, and Sierra’s Infinity
program can be used to answer them
all.

**3.4.1 Sighting in on a Short Target
Range**

A shooter sometimes is faced with the
following problem. He or she would like to sight in a gun for a
zero range of, for example, 250 yards, but sighting in must be done
on a shorter target range, say, 100 yards. The question is where
should a group of shots be centered at 100 yards so that the gun
will be zeroed in at 250 yards?

The answer to this question is straightforward
with Infinity.
A trajectory is calculated using a zero range of 250 yards and using
the altitude and atmospheric conditions at the target range. Then,
the bullet path is read from the calculated trajectory for a range
distance of 100 yards. This is the point where the group should
be centered on a paper target located at 100 yards to assure that
the gun is sighted in at 250 yards.

Of course, any other pair of zero range
and target range distances can be used. It is frequently necessary,
for example, to use a target range distance of 25 yards to sight
in a handgun at a zero range of 100 yards.