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Excellent - more excuses for my bad shooting! :lol:rox wrote: 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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My original question was actually to do adjustments on a scope (which I'm a beginner at), but this is also interesting - My previous TR rifle had a 30" barrel and all adjustment was done on the rear sight; and the raise from 300 to 600 was the standard 10.5 mins...my new TR rifle has a 28" barrel and an adjustable front sight; and the same raise is just under 10 mins...IainWR wrote: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.
Cheers Rox,rox wrote: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).Dougan wrote:Does anyone know exactly what a 'minute' measures at in inches at 200, 300, 400 and 500 yards?
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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The reduced sight radius will probably at least be a contributing factor. You could try entering your current sight radius into my calculator, then reduce the radius by 2" and see how much more the minutes represent. This is only an approximation though; the sight placement on the different rifles could mean that the sight radius difference is not only down to the different barrel lengths.Dougan wrote:...so is that the difference in sight length, the adjustment on the front sight, or both...?
Which rule is that exactly?southern_guy wrote:The rule is most accurate when the sightbase (distance between front and rear sights) is 36 inches!
Indeed. What does work well with a radius of 36 inches is that 0.010" of sight movement equates to precisely 1 inch at 100 yards, which makes it convenient to map a thread with a whole number TPI (Alpha1: TPI = Threads Per Inch) to produce 1 inch of movement per hundred yards - if your sight radius is 36 inches. Which is probably isn't.Gaz wrote:Surely 1MOA subtending 1.047" at 100yds is a mathematical constant?
I measured from aperture to aperture, which was almost bang on 32" (813mm) - Putting this into your spreadsheet increased:rox wrote:The reduced sight radius will probably at least be a contributing factor. You could try entering your current sight radius into my calculator, then reduce the radius by 2" and see how much more the minutes represent. This is only an approximation though; the sight placement on the different rifles could mean that the sight radius difference is not only down to the different barrel lengths.Dougan wrote:...so is that the difference in sight length, the adjustment on the front sight, or both...?
If part of your adjustment is made up of moving the front-sight then it sounds like you might already be combining/adding front and rearsight minutes to arrive at 'just less than 10 minutes'. Remember that they are incompatible. Some are marked in 6 minute intervals and some in 5 even though they have the same pitch!
I haven't thought about a 'rise' as such for years. I just know that at a various distances my front sight is at A, B or C and the rearsight is at X, Y or Z, and that X, Y and Z are all within a couple of minutes of each other.
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