iStrelok  is an efficient and accurate  ballistics calculator for the iOS (iPhone, iPod and iPad)  with user friendly interface. It will come in handy both to casual and dedicated shooters, allowing fast and confident shot placement at medium range(distances up to 600 yds and further with some tweaking). iStrelok is an autonomous software package that once installed, does not require an internet connection to provide full functionality. It is also resource friendly, so you can use it for many hours in the field without excess drain on device battery.
iStrelok features a fast ballistic solver based on G1 drag model and has undergone extensive testing since 2001 by hundreds of qualified shooters.  Supports input/output in Imperial and Metric units. Elevation and  windage adjustments are presented in large and easy to see font for your desired correction in MOA, MRAD(same as Mils), inch/cm and clicks. Instant holdover is visible on a reticle of your choice from a vast reticle database (more are added with each update).  Profiles for rifle and ammo data  are saved, so all you have to enter for quick solution is range and shooting conditions.
Some of the other key features include:

  1. Temperature and barometric inputs
  2. Angle to target inputs
  3. Wind direction and speed inputs
  4. Detailed cartridge data inputs
  5. Customizable reticle variables
  6. Table-based data output
  7. Data export to email

General steps
Once you have iStrelok purchased and installed, perform basic steps for initial setup (explained in detail further if you need clarification):

  1. Configure rifle
  2. Configure ammo

You can now enter target data and atmospheric conditions and get your shot solution by tapping  “Calculate! button.

Rifle Profiles

Configuring rifle profile

Fields are populated with default entries. For entering new data just tap the field you want to change. Tapping numerical value fields pops up a convenient NumPad. Enter the value and be sure to tap “Done” for confirming it.
Rifle 1 - In this field just enter the name you'd like to use to identify this firearm, e.g. “Rem700, .308”
Zero Range - This is the distance to the target that you zeroed your scope at.
Scope Height - This is the height from the centerline of your bore to the center of your sight. To measure it on firearm with a mounted scope, measure the diameter of the scope bell (on the end, from side to side, not the circumference!) and divide that number by 2. Measure the barrel diameter just under or ahead of the scope's bell,  also divide by 2. Last,  measure the gap between the bottom of the scope bell and your barrel. Add all 3 resulting numbers together to get your sight height. Try to be precise since it has direct impact on calculations accuracy.                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                                       
Elevation click - This is the amount of adjustment per-click of your elevation turret. It should be labled on your turret or available in your scope's manual.
Windage click - Same as Elevation Turret, except for your windage turret. This value and unit is very likely the same as the elevation's turret.
These fields can also be used to correct for scope turret clicks that aren't quite what they supposed to be. If you find that your .25MOA per-click scope is actually .23MOA per-click, just put in .23 and you’ll never have to think of it again.
Default click unit is MOA, value is set at ¼ MOA. Unit can be changed to MRAD(MIL), inches@100yards or cm@100meters by tapping a small blue round button just below click fields and selecting needed unit.
Zero Atmosphere – weather conditions when you zeroed the rifle.  It’s a good practice to toggle  the switch to “ON” and input your zero atmospheric conditions. By enabling this feature you get  automatic zero correction when shooting in different conditions. So if you originally zero at 100 meter altitude and then go hunting with that rifle/ammo to 2000 meter altitude, your zero point will be off (how much it will be off depends on how far your zero range was) and iStrelok will account for this.
Altitude - This is your altitude above sea level at time of zero.
Temperature - Temperature at time of zero.
Pressure - Pressure at time of zero.

Adding or editing a Rifle

To add a rifle, tap the "Change rifle" button at upper left middle screen. A popup with 10 possible profiles opens. Select an entry and configure the profile as needed. It shall be saved automatically.
The program remembers all settings data and anytime you select a certain rifle profile will bring it up along with scope reticle and ammo profile used last with this combination.

Configuring ammo profile

It’s basically done the same way as configuring rifle profile.
Catridge 1  - In this field just enter the name you'd like to use to identify this cartridge, e.g. “Barnes TTSX .308, 168 gr”
Bullet weight - The weight of your bullet in grains or grams. This value is necessary only for energy calculation.
Ballistic coefficient – G1 drag model BC value usually is specified by bullet manufacturer or can be found by search on the Internet. One great database can be found  at
Muzzle Velocity - This is the velocity of your bullet when immediately leaving your barrel. It is highly recommended to confirm this using a chronograph. If you don't have access to a chronograph, put in your best guess from a reloading manual or from the manufacturer of your ammo and tweak it until your trajectory calculations match up with your real-world shooting. Of course, this should only be done if you're sure other entered variables such as atmosphere and target distance are accurate. Also you can use Trajectory calibration (Truing) feature to calculate real muzzle speed.


Suppose, you input muzzle speed as 2648 f/s. Shoot at distance bigger than zero distance. Suppose this is 800 yards. Calculated elevation for this distance is 26 MOA.
Find out REAL elevation is needed to hit the target. Suppose this is 27 MOA. On the trajectory validation screen input Distance as 800 yards and Elevation as 27 MOA. Tap button "Calculate" and speed at which elevation will be equal 27 MOA will be calculated. It this case, it will be 2609 f/s. Tap button "Use this velocity" and this calculated speed will replace your current cartridge speed (2648->2609) and screen will be closed. On the main screen tap "Calculate" button and you will get calculated elevation which equals REAL elevation and equals 27 MOA Now you can input any distance and hit the target.
MV temp variationOptional field.Powder burnrate and resulting MV are temperature dependant. You may get higher MVs in summer heat and lower in winter cold. This field specifies in percent how much MV changes within 15 degree temperature change. You can leave the default 1.5% (2,5% for metric units) if you are not sure of you powder properties, or put any  figure   in a range of 0,5-3,5%

Offset relative to first cartridge feature

Sight in with first cartridge in the rifle list. Shoot with second cartridge at the same distance and note vertical and horizontal offset from center. Write this values to the program. Now you can change cartridges without zeroing rifle again.

Adding or editing a Cartridge

Just like with rifle, to add a cartridge, tap the "Change cartridge" button. A popup with opens. Select an entry in the popup and configure the profile as needed. It shall be saved automatically. 10 profiles are possible.


iStrelok now supports a feature allowing Dropbox users to create rifle and profiles on their desktops and sync the device with file uploaded to Dropbox.

Entering Target and weather conditions

After rifle and ammo profiles are created you are ready to get the shot solution.
Range – the distance to your target read from rangefinder, estimated by Mildot reticle or simply your best guess. If you want to create a table, just enter the distance you wish to calculate to.
Wind – enter your estimate of wind speed or data from portable weather station
Wind angle – this is the direction of wind in relation to target. You can enter the degrees (a 12 o’clock wind is coming from 0 deg., 3 o’clock wind is coming from 90 deg. etc) or tap the blue button and just drag the red sector with your finger to whatever side the wind is coming from
Target angle - This is the angle to the target from the perspective of your bore. You can enter a numeric value in degrees, or just like with wind, tap the blue button and drag the the target higher or lower.
Next you may want to input the current Weather. It’s very straightforward:
Altitude – this is your current altitude above sea level
Temperature - Your current temperature
Pressure – Your current atmospheric pressure
If you  tap “Standard values” iStrelok shall automatically enter the ASM (Army Standard Metro) values which are the atmospheric standard for entered altitude, and are used by many bullet manufacturers in calculating bullet BC.


If You now tapCalculate!, the solution is seen in the lower part of the screen in MOA, MRAD, inch/cm and clicks. Just dial it into riflescope turrets and take your shot.
Or if you prefer, tap the reticle to see the holdover.
The reticle view  can be exported by email for printing.
By tapping “Table” You can also bring up a shooting table showing the rifle and ammo profile, velocities, energy, bullet flight times, bullet drop, windage at specified distance increments. All this can be configured in table settings.
The table can also be exported by email for storing, printing etc.



1. If your reticle is placed in first focal plane:
- Tap the "Settings" button on reticle screen and check the checkbox "This reticle is in the First Focal Plane (FFP)
- use it at all magnifications. Holdovers will be the same.

2. If your reticle is placed in second focal plane:
- Tap the "Settings" button on reticle screen and UNcheck the checkbox "This reticle is in the First Focal Plane (FFP)
- Input  Min. magnigifation of the scope
- Input Max. magnification of the scope
- Input magnification the reticle was calibrated for. (Scope manufacturer usually specifies in the manual "power setting for using the ranging features" or «all measurements (subtensions) are valid for X magnification». Use this value).
- Close Settings screen
- set by slider magnification you want and holdovers will be recalculated to this magnification.

What is the difference between a first and second focal plane?

See also: Strelok Pro for iPhone, Strelok Pro for Android

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