Another question for TR shooters

[Dougan]

I have tried googling this, but to no avail, and trying to estimate it from score cards isn't working out...

Does anyone know exactly what a 'minute' measures at in inches at 200, 300, 400 and 500 yards?

[ovenpaa]

1.047 inches at 100 yards springs to mind however I am not near my computer right now to confirm this.

Edit x2 for 200 etc

[Dougan]

Thanks again :cheers:

[Laurie]

ovenpaa is correct - it's 1.047 inches at 100 yards and increases proportionately by distance, so 1-MOA = 10.47 inches at 1,000. Not all target centres are the same size in MOA. Both TR and F-Class use a single target centre for 800 / 900 / 1K distances with the ring diameters correct for 1,000 making them a bit more generous at the shorter distances.

[IainWR]

And do remember that the "minutes" on your sights are a bit nominal. If you move the rearsight forward 2 inches, that shortens your sight radius by about 6%, which in turn makes your "minutes" 6% bigger. That's a change of a bit over 2 "minutes" at typical 1000 yd settings.

Once you know the right answers for your rifle, this only matters if you are trying to compare numbers with someone else, but it is one of a number of factors to consider in getting the best possible setting before you fire the first shot.

[ovenpaa]

Dougan, I would have added more however I was 'typing' on a Kindle in bed and without contacts which involved holding the thing 2" from my nose. Luckily Laurie and Iain added some bulk to my original and somewhat brief answer.

A good rule of thumb is 1" at 100 yards and as it is an angular measurement it is 2" at 200, 6" at 600 and so on. To this day I always round off to the nearest inch in my mind which keeps me on the safe side of things when performing impromptu group measurements.

[rox]

Does anyone know exactly what a 'minute' measures at in inches at 200, 300, 400 and 500 yards?

Mathematically it is 3600*tan(1/60) at 100 yards, which is approximately 1.047" (multiply by 2, 3, 4 & 5 for the specific distances you mention).

In shooting it is very often approximated to 1" at 100 yards.

What you actually get from your rearsight is another thing, and depends on the TPI of the rearsight threads (Alpha1: TPI = threads per inch), and the clicks per revolution, clicks per minute, and the sight radius (between the front and rearsight irises). I once did the maths in order to make my own scorecards with a grid that matched my actual sight movement & radius - the exercise was somewhat pointless, but interesting. I've made a quick spreadsheet that takes the 4 inputs and gives the resulting movement at 100 yards and percentage difference when compared with Mathematical minutes and 'rifle' MOA (1 inch @ 100x). It is initialised with the values for a Trakker with 40 TPI thread and 1/4 minute clicks (from memory). If anyone spots errors let me know and I'll make an update.

http://fbuk.ammara.com/downloads/TR-Rearsight-MOA.zip

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[targetman]

Got that........I think.....now, which way do I twiddle the knobs...??

[IainWR]

And further to Rox's input, the "minutes" on your rearsight and foresight may not be the same!

[rox]

And further to Rox's input, the "minutes" on your rearsight and foresight may not be the same!

Indeed. They should never ever be added together or compared.
Then there's backlash.
And diffraction.
It's a wonder we ever hit the thing at all really.

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