Advancement of Ballistic Programs: The Science of Bullet Flight
By Christopher M. Rance
The red rim of the sun pushes itself over the distant horizon, as a brown haze of dust kicks up from the sniper’s shot. His spotter, with intense eyes, watches the turbulent wake trails behind the bullet (known as bullet trace) through his spotting scope. The sniper calls a clean break, and the spotter watches the impact of the round on the steel target. The spotter records the elevation dialed onto the sniper’s scope turret, the wind call and the range to the target. Prior to taking the shot, the spotter recorded the atmospheric data for the day (station pressure, temperature, humidity and light conditions).
These snipers have mastered the science of external ballistics, which is the science of bullet flight. Their knowledge of external ballistics, along with mastery of the functional elements of the shot process and an understanding of complex engagements, allows the sniper team to hit targets at extended ranges. The sniper team’s success in tactical shooting comes from practice and knowing what tools to use in building an accurate firing solution. The tools that the sniper team will use when applying ballistics in the field can be broken down into three important categories.
- The riflescope. The riflescope is the gateway to the battlefield. In terms of ballistics, the riflescope is an enabler to the sniper. The riflescope applies the calculation via dials or reticles that the sniper needs to engage the target. The riflescope is a precision instrument and in order to use it to its fullest capability, the scope turrets have to be verified, and it has to be mounted correctly. Uncalibrated sight adjustments are one of the most common problems in shooting. In most cases, there is some error in scope turrets. For more information on zeroing and scope calibration, check out my previous article “Sure Kill: A Baseline for Sniper Lethality,” Small Arms Defense Journal, Vol. 10, No. 2.
- Measurement tools. Measurement tools are used to gather the information required to support a scientific calculation. The sniper wants to have the most refined and accurate measurements possible to obtain the most accurate ballistic firing solution. The following measurement tools are important to the sniper: rangefinders (maps, ranging reticles, laser range finders), Kestrel weather meter, angle cosine indicator and a chronograph.
- Ballistic solver. The ballistic solver is the tool that bridges the gap between raw data and useful firing solutions. The basic principle of trajectory modeling is that if the sniper inputs all of the variables correctly into a ballistic program, that program will return an accurate ballistic solution. The sniper has to be aware of the true value of all the inputs. Possible variables that can account for an error in point of impact are shown in the Point of Impact Error Checklist chart. The sniper must ensure none of the listed variables is contributing to an observed vertical point of impact between live fire data and ballistic program predictions.
|Point of Impact Error Checklist|
|Inaccurate Atmospheric Data||Incorrect Muzzle Velocity|
|Error in Zero Range||Error in Sight Height|
|Accounted for Aiming Error at Range||Error in Parallax Setting|
|Uncalibrated Turret Adjustments||Accounted for Wind Speed and Direction|
ATSLAN Ballistic Solver
Atslan from Zikitec® Ltd. is a field-proven ballistic calculator that combines a ballistic solver with a user friendly and very intuitive logbook. The Atslan ballistic solver is specifically designed for snipers and has seen use in Israel by IDF snipers and IDF special forces. Atslan lets you record all your shooting and track multiple profiles, rifles, scopes and ammunition.
Some key features of Atslan are:
- State of the art ballistic calculator with support for: Spin-drift, Aerodynamic-Jump and Coriolis Effect.
- Support for G1 and G7 ballistic coefficients and multi-BCs (stepped BCs).
- Muzzle velocity temperature table.
- Supports imperial and metric units, MRAD (Mil), MOA and IPHY.
- Intuitive functions for: wind direction, azimuth and shooting angle.
- Uses your phone sensors to get barometric pressure, humidity, azimuth, etc.
- Cold bore shot tracking.
- Training performance summary.
- Variety of targets and shooting positions to use for data collection.
- Backup / Restore options.
Muzzle Velocity Temperature Table
Snipers can use the chronograph to create a muzzle velocity temperature table. A minimum of four data points will be needed from the current lot and need to be at least 30 degrees apart. It is always best to have data points for the coldest and warmest points that the sniper will shoot in. A muzzle velocity temperature table is important because a change in the ambient temperature will change the trajectory of a bullet. A temperature change affects the air density which directly affects the ability of the bullet to move through the air. As the temperature rises, the air become less dense and the bullet will experience less drop over range because it is bleeding off its speed at a slower rate. The reverse is also true when there is a drop in temperature, as it will cause the atmosphere to grow more dense, slowing the bullet faster, requiring more time to traverse the same range.
Muzzle Velocity POI Check
After obtaining the muzzle velocity of the cartridge by using a chronograph, it is essential to check the data by confirming the trajectory at a range between 300 and 600 meters using the shorter range for small calibers and the longer ranges for large calibers. Using the POI method to determine muzzle velocity is a good way to check the chronograph as these checks may show that the snipers’ chronograph is habitually giving results above or below the actual muzzle velocity.
Stepped Bullet Coefficient (BC) Method
This is the best way to use a ballistic computer, and Atslan gives you this option. Think of banded or stepped BCs as having a correlating value at the muzzle, at mid-range and at the target. Bullet coefficients are based on not only the bullet design but the velocity. We also know that since the bullet is constantly falling as well as slowing down, that the value of the BC is going to change. A Stepped BC tells the software to adjust the drag curve based on the range and muzzle velocity. Where most ballistic solvers use a single BC number and apply it to the entire flight path of the bullet, Stepped BC corrects the path. Stepped BCs work for both G7 and G1 as well.
Prior to mission and to wrap up their training session, the sniper team conducts the following steps to confirm their trajectory calculations by using predicted firing solutions and observing actual bullet impacts on targets. It is imperative that the ranges to these confirmation targets must be within +/- 1 meter, and all impacts must be able to be spotted to 1/10 of a Mil. The use of a water mark line painted on the steel target can assist in accurate recording of the shots.
The sniper team will:
(1) Dial on predicted dope for 500 meters. Conduct muzzle velocity POI check.
(2) Record vertical POA-POI deviation. Must measure impacts to 1/10 Mil.
(3) Adjust MV if needed. Should not need to adjust by more than 50 fps.
(4) BC POI check. Establish a target near the velocity range between 1350 fps and 1650 fps.
(5) Record vertical POA-POI deviation. Must measure impacts to 1/10 Mil.
(6) Adjust BC until predicted elevation matches observed elevation. Should not need to adjust by more than 5 or 10 points on BC. Annotate environment and wind conditions.
The sniper team has to understand that the shooter influences the bullet as much as every variable that has been discussed. Trust your raw data and always record your actual data in a data book or an intuitive logbook found in a ballistic software application like Atslan. If you cannot get the entire flight of the bullet to line up, make two tracks—a short-range track (supersonic) and long-range track (subsonic). If they work, you solved the problem for the entire path of the trajectory. At the end of the day, the bullet doesn’t lie, and a great sniper will always record and manage a data book. Knowledge and data on previous engagements (DOPE) are vital.
For more information on Atslan, go to zikitec.com