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How do I calculate MOA size and magnification? |
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tpcollins
Optics Journeyman Joined: January/12/2009 Status: Offline Points: 428 |
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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.
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Sparky
Optics Master Extraordinaire Joined: July/15/2007 Location: SD Status: Offline Points: 4569 |
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What scope are you talking about? Is it FFP or SFP?
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tpcollins
Optics Journeyman Joined: January/12/2009 Status: Offline Points: 428 |
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SFP Vortex Viper
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budperm
Optics Retard show me your sheep!! Joined: January/01/2009 Location: Pennsylvania Status: Offline Points: 31710 |
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This sounds like a question for Ilya....
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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson |
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BeltFed
Optics Retard Joined: February/12/2008 Location: Ky Status: Offline Points: 22284 |
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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 out |
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Life's concerns should be about the 120lb pack your trying to get to the top of the mountain, and not the rock in your boot.
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Peddler
Optics God Joined: July/04/2012 Location: Oswego,NY Status: Offline Points: 13526 |
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Don't feel like the Lone Ranger! |
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When you are dead, you don't know you are dead.It is difficult only for others.
It is the same when you are stupid. |
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budperm
Optics Retard show me your sheep!! Joined: January/01/2009 Location: Pennsylvania Status: Offline Points: 31710 |
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unfortunately, Tonto is more my speed.... Hope Edurado isn't put out...
Edited by budperm - August/17/2015 at 05:26 |
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"Peace is that brief glorious moment in history when everybody stands around reloading".
--Thomas Jefferson |
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13181 |
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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
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13181 |
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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
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tpcollins
Optics Journeyman Joined: January/12/2009 Status: Offline Points: 428 |
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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.
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13181 |
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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
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tpcollins
Optics Journeyman Joined: January/12/2009 Status: Offline Points: 428 |
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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.
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koshkin
MODERATOR Dark Lord of Optics Joined: June/15/2004 Location: United States Status: Offline Points: 13181 |
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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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