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subtension of a tard moment

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subtension of a tard moment was created by 13fcolt

So here I sit, spending time on the forums, watching some netflix, and studying my scopes. lebbenB had mentioned a mathematical solution in another thread for deciphering the subtension of a reticles markings at different magnification for a second focal plane scope.
So I went googling for this formula and came up with nothing. I found noting mentioned in any of my scopes manuals or manufacturer websites. I figured either no one uses it or knows about it, or more likely, Everyone already knew and I'm just the last to figure it out.

So I just fell out of the epiphatree and hit every branch on the way down. It's been right in front of me forever and I never noticed it. :banghead: Why is the Highest magnification divisible by the lowest? Smack goes the first branch, Then it all fell into place.
5.5x - 22x
@ 22x markings are 1/2 mil
@ 11x markings are 1 mil
@ 5.5x Markings are 2 mil
so I can still dope with these known values as if I had FFP. Now all I need is mil turrets to take out that nefarious conversion and I am good.


except for the leupolds. they use a 3.1 magnification ratio so I guess the increase would be as such. that ones not adding up the same so I'll have to get back to you.
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11 years 5 months ago #13188

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Replied by Akai on topic subtension of a tard moment

What about the wind and temp, got ant ideas on that :pray:
AKAI
11 years 5 months ago #13192

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Replied by 13fcolt on topic subtension of a tard moment

yeah, what was it you needed help with?
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11 years 5 months ago #13199

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Replied by LebbenB on topic subtension of a tard moment


DUDE! I so totally forgot to answer your question. Please forgive me.

You've over-thought the formula. Let's say you have a mil-dot reticle in a 3-10x SFP scope. The reticle is "True" at 10x. At 5x, multiply the mil reading by 2, at 3x you multiply by 3.33.

If the reticle is "true" at a lower magnification, you would divide the mil reading at higher magnifications vice multiplying.

Sorry, bro...Sometimes I get CRS.

Wind Formulas
Mil: wind speed x bullet drift = Correction

Drift calculations: 100m - .003 mil
500m - .008 mil
1000m - .019 mil

MOA: Range (first digit) x Wind Speed = Correction

For a half value wind, multiply the correction by 2

Temps
For every 20 degree change in temp from the temp on the day the rifle was zeroed, add or subtract 1 MOA/.4 mils.
RLTW
The following user(s) said Thank You: 13fcolt
11 years 5 months ago #13212

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Replied by 13fcolt on topic subtension of a tard moment

No worries brother. I honestly hadn't waited for any response, I was looking it up as soon as you had mentioned it.
I do over think this stuff all the time trying to get my head around it. As I frequently find myself more preoccupied with digits and decimals, I miss my blissful ignorance of simpler times when guestimating holdover and shooting by feel was good enough.

Thank you!
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11 years 5 months ago #13224

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Replied by Sharkey on topic subtension of a tard moment


Oops, thought someone said my name...lol

You guys just go on talking french and I'll, um, watch spongebob or something for a while... :laugh:
11 years 5 months ago #13226

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