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Data Entry:
Each
of the fields on each of the forms display the “current record” data from
the database. The user should edit this data on a field-by-field
basis as needed to create the desired set of data. The changes made by the
user will automatically be saved when the user exits the program or clicks
OK in the “Program Manager”.
There are two primary options for editing data in
Exbal.
First there is new "quick digit
keypad" located at the bottom of every form. The field in focus
(flashing vertical bar) will be replaced by any digits and decimal point
that the user inputs using tapping the buttons. When all of the digits and
decimal point is entered, the user MUST tap the "enter" button.
Secondly, the Palm Keyboard Emulator
can be used. Data entry is completed
by tapping on the "done" button on the emulator window.
Bullet Data, Field Conditions, Target
Data, And Results
Each of the three primary forms has fields to enter data and push buttons
to move onto the next logical form or to return to the main form and
menu. The first logical form is the “Bullet Data"
form, which has fields to specify bullet weight, sight in distance,
distance between line of sight and line of bore, and the ballistic
coefficient of the bullet. A check
box is used to specify that the sight in distance should be meters rather
than yards. Push buttons are used to go to the next logical form or
to the main form.
The second logical form is the “Field
Conditions” form, which has input fields to specify
muzzle velocity and current atmospheric conditions at the target location.
These include altitude, temperature, pressure (not corrected to sea level),
and relative humidity. A check box is used to indicate that system
should calculate pressure based on altitude.
The
third logical form is the “Target Data”
form, which has input fields to specify target distance, wind speed, wind
direction, target speed, and incline angle to target. A check box is used
to specify that the target distance should be meters rather than yards. A
push button is used to start the ballistic calculations. Another push
button is used to return to the main form and menu.
Bullet Data
Field Data
Target Data
Ballistic Coefficients
Optional Input Forms
Sight In Data, Ballistic Coefficients, Sight Adjustment Options
Three optional forms are provided to enable additional
specifications. The "Sight In Data" form is used to
specify the conditions at the time that the rifle was sighted in which may
be significantly different than the conditions at the target location. There are input fields for muzzle
velocity, and atmospheric conditions at the time of sight in. A check box (automatically set by
default) is used to indicate that the sight-in conditions are the same as
those specified under “Field Conditions” above.
The multiple "Ballistic Coefficients” form is used to
specify bullets that have ballistic coefficients that change with velocity.
Examples of these are the high efficiency Sierra MatchKing target
bullets. The 30 caliber 168 grain MatchKing is illustrated in the
following display.
The interpretation of this data is as follows: For velocities exceeding 2600 fps the
ballistic coefficient is 0.462, for velocities between 2600 and 2100 fps
the ballistic coefficient is 0.447, for velocities between 2100 and 1600
fps the ballistic coefficient is 0.424, and for velocities less than 1600
fps the ballistic coefficient is 0.405.
There is an excellent discussion in the Sierra Reloading Manual of
how the need for multiple ballistic coefficients was discovered.
The fact that the ballistic coefficient changes as velocity changes is
taken into account when Exbal performs the ballistic motion equations.
The "Sight Adjustment Options" form is
used to specify the units of sight correction for elevation, windage, and
target lead (for moving targets). In the display of results, both inches
and “clicks” are displayed. The default units of sight adjustment (clicks)
are one minute of angle (approximately one inch per hundred yards). Many target scopes have dial readings for
windage and elevation in minutes of angle. Other scopes have click stops
for 1/8, ¼, ½, or one minute of angle. Still other
scopes have internal gradient lines or dots to indicate minutes of angle
and/or mil-radians (mil dot).
Sight Adjustment Specifications
Sight-in Conditions
Exbal
provides two output windows. The "calculate" button shows the
ballistic data for the specified target. It contains all of the information
about the bullet at the target point. The "drop table"
button provides the sight adjustment data needed at a series of target
distances.
Calculation Results
Drop Table
Exbal Utility Functions
Three
"utilitiy" functions are provided to enable the shooter in the
field to make adjustments. First there is the Match Sight-in Point
function which calculates the true zero point based on the bullet impact at
a specified distance. Second there is the Trajectory Correction
Function which uses a known sight-in distance (zero point) and
calculates the velocity that matches impact point at a known
distance. And finally there is the Range Estimation Calculator
which does the math associated with using a ranging reticle to estimate
target distance.
Match Sight-in Point
Trajectory Correction
Range Estimator
Data Manager
The
“Data Manager”
form contains push buttons to enable the user to develop and migrate
through a database of records.
The “Record Name”
field displays the name of the current data record. The name is initially
assigned by the system when a new record is created. It can, and
should be changed by the user and then saved by tapping the “OK”
button. Any changes made to the current record using the forms
discussed above will be maintained in the database.
The “Record
Number” field displays the record number of the current data
record. It is assigned by the system. The “New Record” button is used to
create a new record. It will be pre-loaded with a copy of the current
record and given a title <no name>. The user should change the name
of the record to update the name, and then edit the data using the forms
discussed above.
The “First” button moves to the first record in the database. This is
record number one. The
“Last” button moves to the last record in the database. This is the highest
record number currently on file. The “Next” button moves from the current
record to the next record (record number will be one more than the current
record number) in the database unless the current record is the last
record. The
“Prev” button moves from the current record to the previous record (record
number will be one less than the current record number) in the database
unless the current record is the first record. The “Delete” button (USE
WITH CAUTION) will delete the current record from the database
and move to record number one. The “OK” button updates the current
record name in the database and returns to the main form.
Ballistic Reticle
Analysis For The Palm Version of Exbal:
Scopes
with ballistic reticles are increasingly being used by long range shooters
and they have been used by military "snipers" for many
years. They offer an alternative to
making external scope adjustments to compensate for bullet drop at longer
ranges.
The concept of the ballistic reticle is introduced on http://www.perry-systems.com/reticle_analysis.htm
web page. A ballistic reticle consists of a main cross-hair and a
series of aiming reference points (bars, circles, or dots) which are spaced
along the vertical cross-hair.
Information about specific reticles can be obtained from
Swarovski/Kahles, Burris, Leupold, Nightforce, and other vendors who offer
them with their scopes.
To illustrate this concept, the set up window and point blank range
analysis results are shown for a 308 Win, 175gr MatchKing bullet at 2600
fps, sighted in at 100 yards, shooting at a target 600 yards away. The reticle being illustrated is a
Nightforce NP-R2 reticle, which has 10 reference bars spaced at 2 MOA
intervals.
The Point Blank Range results for this particular case indicate that Bar #8
should be used. (the zero point for Bar #8 is 592 yards so the bullet
will strike about 2 inches low) The beauty of this approach is that
no external scope adjustments were needed.
Ballistic Reticle Analysis
Point Blank Range Analysis
Now
the Palm version of Exbal will calculate how the use of a ballistic reticle
will affect the bullet impact point compared to the aiming reference point
used. There are new windows to
support this analysis. The first window enables the user to select retcle
data from a list of reticles. The second window is used to manually specify
the configuration of the ballistic reticle being used. This is where the measurement system
(MOA, IPHY, or MILS) and the angular difference between the main cross-hair
and each of the aiming reference points (bars, circles, or dots). For simplicity the reference points are
labeled Bar #1, Bar #2, etc.
There are three different measurement systems used to specify the angular
difference between the horizontal cross-hair and the aiming reference
points (bars, circles, dots). First
there is the traditional "minute of angle" or MOA which is equivalent to 1.048
inches per 100 yards. The second
system is "inches per 100 yards" or IPHY. And the third
system is "mil-radians" or MILS (1 meter per 1000 meters) which is equivalent to 1 yard
per 1000 yards or 3.6 inches per 100 yards.
Ballistic Reticle Selection List
Edit Reticle Specifications
Two
optimization functions have been added. The first function determines
what sight-in distance should be used so that a particular bar will strike
the target center at the specified target distance. The second
function determines what operating power the scope must be set at to
achieve making the zero point of the specified bar equal to the target
distance. The second function is only applicable to scopes that have
the reticle in the second focal plane. If the spacing of the bars or dots
remains constant while the image size changes with power, the reticle is in
the second plane.
Calculate Optimum Sight-in Distance
Calculate Optimum Power Setting
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