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How do I calculate MOA size and magnification?

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 07:19
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I was shooting recently at a target with a bullseye a bit under 3/4" (let's say .7") at 70 yards away. The scope's reticle has a 1 MOA dot for the crosshair and the 2.5-10 power scope was set on 4x. The 1 MOA dot seemed to cover the .7" bullseye perfectly but is there a formula to calculate this? 

1 MOA would be about .7" at 70 yards as well, but I'm trying to correlate a .7" bullseye at various magnifications. Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 09:20
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What scope are you talking about? Is it FFP or SFP?
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 10:33
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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 10:46
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This sounds like a question for Ilya....
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 10:52
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Originally posted by budperm budperm wrote:

This sounds like a question for Ilya....

I don't know. I think any of the smart guys like Riflrdude, supertool, or some of the others could answer it. It just leaves you and me outBucky
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 11:52
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Originally posted by BeltFed BeltFed wrote:

Originally posted by budperm budperm wrote:

This sounds like a question for Ilya....

I don't know. I think any of the smart guys like Riflrdude, supertool, or some of the others could answer it. It just leaves you and me outBucky


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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 12:10
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unfortunately, Tonto is more my speed....  Hope Edurado isn't put out... Smile

Edited by budperm - August/17/2015 at 05:26
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 12:30
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A 1MOA dot for a reticle calibrated at 10x would be 2MOA at 5x and 2.5MOA at 4x.

2.5MOA at 70 yards subtends 1.919 inches.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 12:35
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Now that I think about it for a moment...

The only 2.5-10x scopes in the Viper line up are the 2.5-10x44 SFP and 2.5-10x32 FFP models.  Both are available as PST and HS or HS LR products.

I do not think any of them have a 1MOA crosshair.

Or are you talking about the crossbow version of the 2.5-10x44?

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 13:37
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Originally posted by koshkin koshkin wrote:

Now that I think about it for a moment...

The only 2.5-10x scopes in the Viper line up are the 2.5-10x44 SFP and 2.5-10x32 FFP models.  Both are available as PST and HS or HS LR products.

I do not think any of them have a 1MOA crosshair.

Or are you talking about the crossbow version of the 2.5-10x44?

ILya



Originally posted by koshkin koshkin wrote:

A 1MOA dot for a reticle calibrated at 10x would be 2MOA at 5x and 2.5MOA at 4x.

2.5MOA at 70 yards subtends 1.919 inches.

ILya


Yes, the XBR for crossbows. 

That makes sense, but still doesn't explain why it barely covered the less than 3/4" diameter bullseye at 70 yards. Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 13:49
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How did you determine that it barely covers a 3/4MOA bullseye at 70 yards?

If you overlay a 1.9 inch reticle feature on top of a 0.75 inch bullseye, the bullseye is completely covered.  However, in order to see the edge of the bullseye, behind the reticle dot, the line of sight only has to shift by 0.58 of an inch or by  ~0.8 MOA.

Unless you are staring at it from an exceptionally sturdy set-up, that is not a whole lot of movement.

Now, if the eyepiece is not set-up quite perfectly, you might even have an MOA or so of parallax error at that distance, so you can see the bullseye by simply shifting your eye behind the scope.

ILya
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 14:25
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I'm going to have to walk that back. I set up the same target in the neighbor's yard and with my crossbow pointed out from the garage (I'm surrounded by liberals), it did cover the two marks that were 1" each side of the bullseye - duh.

For whatever reason, I was trying to use the 3/4" bullseye as being 4 times closer at first and then I got to thinking that 3/4" is still 3/4" no matter how far away it is and got confused even more! Thanks for the explanation.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/14/2015 at 14:29
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Everyone gets confused when they start dealing with linear units too much.  When you talk about aiming, stick to angular units (MOA or mrad) in this case and it will all come together much better.

ILya
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