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The Trag1s5 (for PC) from Horus Vision illustrates the key inputs of ballistic calculators for long range rifle shooting – gun data, atmospheric data and  target data.  The output is an aiming solution for a scoped rifle – elevation and windage adjustments.

Introduction
Having a riflescope capable of elevation adjustments to 1500m or more is one thing, but it is entirely a different matter in knowing what elevation and windage adjustments to make, in order to get a first shot hit.  This article will look at three sets of ballistic calculators that provide firing solutions for long range shooting:  the Nightforce Ballistic Program for PC and Nightforce Ballistic Program for Pocket PC, both more commonly previously known as Exbal; the Trag1s5 for PC and ATragMX for Pocket PC from Horus Vision; and the Precision Shooter’s Workbench for PC and Field Firing Solution for Pocket PC from Lex Talus Corporation.

Military snipers teams have been calculating aiming solutions using pen, paper and electronic calculators for decades.  But it has only been in 2009 where the US Army and USMC have adopted widespread use of ballistic calculators – an order for more than 7500 Recon PDAs with ATragMX.

Generally, most shooters will chose to use a ballistic calculator on either a PC or PDA.  The advantages of PC versions are that they generally provide much more data, which can be beneficial to those who develop loads.  They are also designed so that ballistic data cards can be printed and taken into the field.  Their disadvantage is that the field conditions may vary from those that were input.  PDA versions eg Pocket PC and Palm OS, are designed to be taken into the field.  The advantage is that the firing solution is likely to be more accurate than a printed ballistic data card, because the inputs will be the most accurate eg exact range, and most up to date eg wind and temperature.  Their disadvantage is that it’s more kit to carry and batteries can go flat.  Depending upon the degree of field use the PDA may need to be waterproof and dustproof, but must have a screen that is readable in direct sunlight.

Exterior Ballistic Data
Each of these ballistic calculators is slightly different in the data that can be input and the data that is then presented.  But in general you enter information about the rifle and ammunition, atmospheric conditions, and target data.  An aiming solution is then calculated for the elevation adjustments and windage adjustments for the rifle scope eg mils or moa or clicks for the turrets.  Technically, these ballistic calculators cover exterior ballistics – from the point the bullet leaves the muzzle, until it hits the target.  They do not cover interior ballistics (what happens to the bullet before it leaves the barrel), nor terminal ballistics (what happens from the point the bullet hits the target).

The rifle and ammunition information typically requires; calibre, bullet grains / weight, ballistic coefficient of the bullet, muzzle velocity, rate of twist in the barrel and height of the rifle scope above the barrel.  The bullet information is usually available from the manufacturer, but muzzle velocities at various temperatures can be found by firing through a chronograph. 

These ballistic calculators have two methods of entering atmospheric data.  The first option is to enter the altitude and temperature.  The second, and far more accurate method, is to enter the station pressure, the temperature and relative humidity. 

The key to understanding how these ballistic calculators work is that they make adjustments based on the Standard Metro model (and not ICAO) which is shooting at mean sea level, with a station pressure of 29.53 inHg, a temperature of 59F, and a relative humidity of 78%. 

Station pressure is the actual barometric pressure that exists at the shooting position (altitude), which is different from the barometric pressure that is presented on weather maps (which is adjusted to mean sea level).  For example, say you are shooting at an altitude of 700m.  The air pressure (station pressure) will be lower than if shooting at an altitude of 100m, so all other variables being the same, the bullet will travel further at the 700m altitude (less air pressure means less resistance). 

The first option is where perhaps the only equipment available is a map and a thermometer.  The second option is perhaps where there is a portable weather station such as a Kestrel 4500NV, which can provide all the atmospheric data plus information about wind speed and wind direction.

Each of these ballistic calculators can handle inputs in either metric or imperial measurements eg temperature in Celsius or Fahrenheit.  The ATragMX also allows a dual setting of atmospheric data in imperial and range in meters.

Target data typically includes inputs for wind speed and direction (clock based), elevation angle, target range, and target speed.

Ballistic Coefficients
Each of the three calculators is a proprietary product and while using the same principles, they do differ in their inputs so if the same data is input to each calculator the results do differ slightly.  This doesn’t mean one is more accurate than another one, but it does mean that it may be necessary to tweak the calculated solution to what occurs in the field. 

The ballistic coefficient (C1) is a measurement of the bullets’ efficiency to travel through the air, with 1 being perfect.  C1s are published by manufacturers but can also be calculated.  ATragMX can calculate BC by either bullet drop, or by muzzle velocity at two ranges eg firing through two chronographs.

To fine tune Nightforce and ATragMX the C1 is changed directly, whereas with PSW and FFS the C1 is left unaltered and the Deceleration Constant is changed. (DK).
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Nightforce Ballistic Program - PC version

The primary screen of the Nightforce Ballistic program for PC illustrates the data inputs and ballistic data output from the calculation in a table format.

Nightforce contains two particularly useful options: Reticle Analysis and Point Blank Range.

The Reticle Analysis option permits the entry of characteristics about the reticle in the rifle scope, which then calculates the ranges associated with the various hack marks on the reticle at the zero settings.  This is great for shooters with mil-dot type reticles who prefer to hold-off (rather than make adjustments for elevation).

The Point Blank Range option provides information for point blank shooting.  PBR is the maximum range where a shot fired at a target of a certain size will hit that target, regardless of the actual range within the PBR.  Basically the apogee of the bullet is always less than the top of the target.  This is also known as the danger range.  Knowing the PBR allows a shooter to take snap shots (without making any adjustments for elevation).

Trag1s5 - PC version
The Trag1s5 provides an excellent visual reference for the Horus Vision reticle system and is great for familiarisation with the Horus system and for demonstration of the aiming solution to first-time users.

Precision Shooters Workbench - PC version

The primary screen of the Precision Shooters Workbench for PC illustrates the data inputs and ballistic data output from the calculation in a table format.  The Atmosphere Files, Turret Files and Bullet Files can all be stored individually.

The Precision Shooters Workbench contains a wide array of possible columns that can be added and re-arranged according to user preference.

Pocket PC Versions

Nightforce, ATragMX, and Field Firing Solution Pocket PC versions showing screens for firing solutions.

Nightforce, ATragMX, and Field Firing Solution Pocket PC versions illustrating screens for target and wind inputs.

The number of inputs for wind is a key area of difference between the three Pocket PC ballistic calculators.  Nightforce has a single wind input ie at the firing point.  ATragMX has up to two wind inputs ie a low and high wind bracket at the firing point.  Field Firing Solution has up to three wind inputs; at the firing point, mid range and at the target.

Another key difference is for multiple targets.  Nightforce has a single target, ATragMX has up to four targets from a single firing point, and Field Firing Solutions can have numerous targets and numerous firing points.

Each of these ballistic calculators can or does include spin drift in the firing solution.  Spin drift is the effect a spinning bullet has.

When shooting past 800m Coriolis, the spin of the earth, also comes into play.  For example in the three seconds it takes a bullet to travel 1500m the target may have moved by about a metre.  Nightforce does not make allowance for this, but both ATragMX and FFS can include Coriolis in the firing solution.  To include Coriolis it becomes necessary to input a selection for north or south hemisphere, the latitude, and the compass direction of the shot.

Nightforce, ATragMX, and Field Firing Solution Pocket PC versions illustrating screens for range estimation using target size and reticle image size.

The methods available for range estimation also differ between the systems. 

Nightforce has a Range Estimation option.

ATragMX has options for Range Estimation and Target Speed Estimation. 

FFS has Ranging options for Direct, GPS, Map and Reticle. A GPS can be used to enter positions at Firing Points or Target Reference Points.

Favourite Features

Nightforce, ATragMX, and Field Firing Solution Pocket PC versions illustrating screens for some  options and functions.

There are things I really like about each of these ballistic calculators. 

• Nightforce is easy to use and the Point Blank Range and Reticle Analysis are very handy. 
• ATragMX is very intuitive to use and because I use a Horus reticle in both my riflescope and spotting scope it is what I primarily use in the field and it is fast to operate. 
• The multiple target abilities of Precision Shooter Workbench and Field Firing Solution provide a great method of planning and recording shooting stages for matches. 
• The factory ammunition / bullet databases in Nightforce and PSW / FFS provide a handy mechanism to lookup and set-up firing solutions for other people in the field.

Software Media
The Nightforce products are purchased separately, and are provided on CD, with the Pocket PC version loaded via ActiveSync.

The Horus Vision products are purchased separately.  Trag1s5 is provided on CD.  ATragMX is provided either on SD card or CF card and is copy protected (cannot copy to Pocket PC memory).

The Lex Talus products are purchased as a bundle (ie PSW and FFS) which is downloaded to PC, and the Pocket PC version loaded via ActiveSync.  These are also available as a trial download.

Mildot Master
The Mildot Master is a slide-rule analogue ballistic calculator that is very simple to use.  The only preparation necessary is to paste bullet drop information for the ammunition being used (onto the back of the Mildot Master), and to tie on a piece of string with a split shot at the end.  If you use metric adjustments and metric ranges purchase the additional metric slide insert.

Screenshots relate to the following versions:

Trag1s5 Version 1.1.2
Exbal Version 9
Precision Shooting Workbench (c) 4.0.2.19
TragMX Version 3.79
Exbal Version 6.0 Build 2579
FFS-Delta III (c) Version I3 4.0.2.28