The Goal

The Goal

Sunday, 31 May 2015

Thoughts on SCATT's F-Coefficient

There is a setting in the SCATT "shot parameters" menu with the name F-Coefficient, which appears to cause a lot of confusion for people. This parameter simulates the effect of muzzle movement on the outcome of the shot and should be set appropriately depending on which discipline you are training for. The "right" number for fullbore seems to be somewhere in the region of 30-40 however this is based on subjective experience and not a hard numerical analysis.

The F-Coefficient setting is found in the Shot Parameters menu.
Why is this important?
When a shot is fired the amount and direction of muzzle movement will have a significant effect on the fall of shot. If the muzzle is moving as the shot exits the bore then the bullet will continue to move in the same direction as it flies down the range (Newton's 1st law of motion.) The slower the movement of the muzzle, the less the shot will be pushed out from the centre of hold. Bullet velocity, distance to target and other factors will also affect how big the effect is.

SCATT attempts to simulate this effect. Manipulating the F-Coefficient allows the user to tune how far the shot is thrown to simulate their discipline.

F-Coefficient Effects
The three diagrams below show the effect on the fall of the same shot with F-Coefficients of 0 (zero), 37 (the value I usually use) and 75 (the default value, which is supposed to match 50mtr smallbore.)

The effect of different F-Coefficient values on the same shot.
As is clear from the diagram, increasing the F-Coefficient value increases the distance from the point of aim when the shot breaks (visible on the diagram where the grey-blue trace meets the red trace.) Where the F-Coefficient value is zero, the shot falls exactly where the rifle was pointing when the shot was fired. As the value is increased, the shot falls further away from this point. Note that the direction in which the shot moves is the same as the muzzle movement as the shot breaks, shown by the end of the grey-blue trace.

Suggested F-Coefficient Values
For fullbore I generally use an F-Coefficient value of 37, which seems to correspond best to what I would expect to see during a real shoot*; however any value in the range 30 - 40 would seem to be fine to me. Note that if you want to compare different SCATT files, you should set the F-Coefficient to the same value!

That said other shooters have alternative views on what F-Coefficient setting should be used. Most of these are simply a debate between which value seems to simulate a particular discipline the best; however one alternative method is to set the F-Coefficient value to 0 (zero) and use the "speed" tab to assess individual shots. I've never tried this approach as it seems overly complicated to me, but you may prefer it.

Get that SCATT out and start doing some training!

* The best way to determine the right F-Coefficient value for fullbore would be to do combined livefire / SCATT to compare the simulated fall of shot with the real fall of shot; however as this is not recommended with the SCATT USB Professional on a centrefire rifle (SCATT's newest model, MX-02 supports this but I don't have a GBP1200 to spare at the moment to try it out!)

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