Getting the Best Accuracy from a G2-ShootersPac

This article will tell you how to get  the very best possible accuracy from your system.

In many practical use-cases of your SMT G2-ShootersPac you can skip some of the fussier steps here and still get results "good enough" for your purposes and that is the subject of another article.  But if you need or want the highest achievable measurement accuracy, read on....

To get the best possible accuracy requires attention in three areas

• setup
  • locations of sensors on target frame
  • perpendicularity of chrono mic to target face
  • plumbness (verticality) of  target face
  • temperature sensor shaded from sunlight
• calibration/validation
  • verify all sensors working (tap test)
  • verify temperature sensor calibration correct
  • calibration shots to correct for any errors in placement
  • verify calibration
• use
  • perpendicularity of shooter to target face (no firing from side-angle)

This sketch shows an ideal installation of the sensors on the target, and the ideal direction for shooting (incoming bullets directly perpendicular to the target face and sensor plane):

If any of the above are wrong or poorly done your e-target will still work, but every shot it reports will contain a systematic error.

Rule 1 is TRY FOR PERFECTION in your setup; the better your setup the better your measurements will be.

Rule 2 is IF YOU CAN'T MAKE IT PERFECT, ASK SMT FOR ADVICE.  There are some systematic imperfections that can be compensated-for in software; when in doubt, consult with your SMT dealer and ask for help.
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Here are detail descriptions of the above points

locations of sensors on target frame
The mic sensor mounting plates are expected to be in a "rectangular geometry", that is to say the horizontal and vertical spacings between the mics can be different, but they need to be set up in a perpendicular manner.

Please measure your horizontal ("WIDTH") and vertical ("HEIGHT") spacing to within 10mm.

perpendicularity of chrono mic to target face
This is the single most important item to get correct.  This can be a very fussy thing to set up correctly but it is well worth your while to get the front mic (#3) within 2mm of being perfectly perpendicular to the target face, in both the horizontal and vertical directions.

If necessary, shim or otherwise adjust your mounting plate until the front mic and rear mic are as close to perfectly perpendicular as you are able to achieve.

plumbness (verticality) of  target face
The ideal orientation for the target face is perfectly vertical.

If this is not possible, a small but constant tilt angle is the next best thing.

The most troublesome setup is on a moveable target carrier mechanism that has a certain amount of "slop", that allows the wind to blow the target face so that it tilts backwards or forwards, and produces a variable (and unknown!) angle of tilt.  If possible, shim or wedge the target carrier frame to minimize or eliminate fore-and-aft tilt angle changes.

temperature sensor shaded from sunlight
A correct temperature reading is required in order to accurately calculate shot position.  The temperature sensor element (the fourth lead of the main branch of the wiring harness, which does not have a BNC connector) should be placed in a location in which air is able to flow over it freely, but it must not be exposed to direct sunlight - otherwise the temperature will vary by up to 15C depending on the intensity of the sunlight falling on it.

Arrange for the temperature sensor to be shaded for the duration of your shooting.

verify all sensors working (tap test)
You can do this at home, or you can do this on at the range as you are setting up your gear getting ready to shoot.  When you are in the ADMIN -> TARGETFRAME menu, very lightly tapping a microphone sensor element with your fingernail will cause the microphone to fire and a large green number (e.g. "4") to display on your screen for several seconds.  This confirms that the mic and all harness wiring are fully functional.

verify temperature sensor calibration correct
This can be done as part of the "tap test".  Examine the temperature that is read when you tap a mic, and confirm that it is within 1-2C of the correct air temperature.

calibration shots to correct for any errors in placement
Any fixed offset errors of the target face paper relative to the physical centre of the sensor array can easily be measured and completely compensated for by firing a shot near the middle of the target (10-ring/5-ring or better) and entering the measured shot location.  After this

​verify calibration
After your system is properly set up, is reading the air temperature correctly, and has been calibrated, you can easily check to see if you are experiencing systematic errors or not.

• Fire three shots at the target
  • one shot about 500mm or 20" left of centre (9-o'clock)
  • one shot about 500mm or 20" right of centre (3-o'clock)
  • one shot about 500mm or 20" above of centre (12-o'clock)
• Examine the e-targets reported bullet speed at the target.  This should be within 50fps of the speed that you expect, based on a properly done ballistics calculation (incorporating your known muzzle velocity, your bullet type, your altitude and air temperature).  If your bullet speed is not as expected, something is crooked - your chrono mic, or your target face, or the shooter relative to the target.
• Compare the e-target's reported bullet position versus the bullet holes in the paper.  If the e-target is reporting positions consistently inboard of the actual shot holes in the paper (or consistently outboard of the shot holes in the target paper), either the measure air temperature is wrong or something is crooked - chrono mic, target face or shooter.

perpendicularity of shooter to target face (no firing from side-angle)
The shooter should be firing directly at the target in a perpendicular manner.

If this is not possible (some ranges are built "crooked"), it is possible to correct for this in software - please consult with SMT for details on how to measure this and how to configure the software accordingly.
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