Correcting Subatentions For Magnification at Various Powers

[Humb1e_1]

Morning all,

I've finally got my kit sorted and am now looking to get stuck in to shooting.

I was advised to get a SFP scope so the crosshairs won't block the target, seeing as I'm shooting known distances.

The substentions on the reticle are accurate at 18x magnification. Is there a way to convert the substentions so I can estimate at 24x magnification etc. The internet has provided answers for magnifications that are half or double of the correct magnification.....

Cheers in advance for any help.

Humble

[WelshShooter]

Think about it logically. So at a higher magnification, on a FFP scope the subtensions will grow apart, and a lower magnification they will squeeze together. From the point of view of a SFP scope, you would say that at higher magnifications, the fixed subtensions need to be smaller since the spacing between subtensions would be bigger, and at lower magnifications the fixed subtensions would need to be bigger since the spacing between subtensions would be smaller. With this in mind, the following formula should apply.

Subtension_actual = Subtension_reticle x (Magnification_calibrated / Magnification_used)

Where Subtension_actual calculated is what the Subtension_actual should be,
Subtension_actual reticle is what you read on the reticle,
Magnification_calibrated is the power that you subtensions are calibrated to,
Magnification_used is the power you have set.


Let's use an example. Using your given information, you want to know when you set your power to x24, what does the 4moa reticle actually read? Using the formula above:

Subtension_actual = 4 x (18/24)
Subtension_actual = 4 x 0.75
Subtension_actual = 3

Another example, what does 10moa on a reticle measure as when using a power of 8?

Subtension_actual = 10 x (18/8)
Subtension_actual = 10 x (2.25)
Subtension_actual = 22.5

Remember the logic part and understand what is going on, and it's easy to recall or figure out the formula.

[Humb1e_1]

Hi Welshshooter,

Thanks for that. Now I've had that explained it makes perfect sense. I had got to the 0.75 but was sure if it should then be multiply or divide.

So if using 24x, for all intensive purposes, I can just use 75% of the the required value at 18x.


Appreciate the help!