Rifle Scopes help with mil-dot calculations….casue I am brain farting

[ker2222]

So….in spite of years of public education and higher education…..i am absolutely confounded and uncertain.

I am making a range card for a second focal plane scope. It mils correct at 12x. I would like to add a column on my range card for the mil holds at 20x so I don't have to do the math……and I can't figure out the formula to do so……

for example: A 1 mil hold @12x is what at 20x???


can someone help…..

 

[TheJ]

If my engineering degree isn't failing me, the following formula should work for you.

Mils * (Mil Mag / Current Mag).

So if your hold is 2 mils @12x (your mil magnification) and you want 20x you do:

2 * ( 12 / 20 ) = 1.2 mils

Ranging / sizing with the reticle should use the reverse formula.

 

[roggom]

To OP, Not really, because the subtension is specific to the scope. You will have to consult your operating manual to find the proper subtension at those two ranges and then do the math.

If you can not find the info, find a true mil target ( can be found by searching or here Storm Tactical FREE Downloads, Targets, Sniper Rifle, Precision Rifle, Storm Tactical University)

Go to a range and setup for 100Y, at x12 your the mildots on your reticle should match to the circles on the target. Then move the magnification ring to 20 and see where it ends up. I would find a place on the ring where the reading is x2 to make things easier.

At x12 the dots will match up to 1 mil, as you move up in mag the image will become larger to a point where the target image takes up 2 mils. At that point your range will be x2 what you are reading. Mark that on your scope ring. If you scope moves to a lesser amount, you can reduce below x12 and find the 1/2 point.

The math may work out on paper, but it is common with SFP scopes that the true x1 focus is not at the ring setting, but a little above or below.

 

[colscar]

my advise to you is just leave it at 12 power and be done with it i have a sfp also and i leave that thing at 10x when ranging.... if i need to zoom in more i do but for what i do i just leave it there ... keep is simple and dont kill yourself over it

 

[09jisaac]

my advise to you is just leave it at 12 power and be done with it i have a sfp also and i leave that thing at 10x when ranging.... if i need to zoom in more i do but for what i do i just leave it there ... keep is simple and dont kill yourself over it

He is asking for a solution for a specific problem.


@ OP, TheJ and roggom are both correct.

Theoretically a mil should be twice as much on half the power and half as much on twice the power. So if 12x=1mil, 6x=2mils, 24x=.5mils and 20x=.6mils. If you are sure your scope is correctly marked then you are done there.

But:

With most scopes the magnification does not match the mag ring exactly. You need to find on your scope exactly where it matches up. Some scopes may be way off. When you find the specific spot, mark it.

If you can hold the firearm steady, it is easy to do. Either print out a target in mils, or take a piece of poster board (anything really) and draw a big plus sign with a wide tipped sharpie. On one side mark for mils every 3.6inches (or 10 centimeters) and on the other side mark for your 20x correction of .6mils at 2.16 inches (6 centimeters). Set this target 100 yards away if using inches, or 100 meters if using centimeters.

I have usually have problems printing things to the right size, so the poster works better for me.

Also, when you are done with that you can shoot the target to see if your scope's internals are correct. You can see if a dialed mil equals a mil and if you were correct on your 20x mark.

Hope this helps and that my math was correct.

 

[TheJ]

To OP, Not really, because the subtension is specific to the scope. You will have to consult your operating manual to find the proper subtension at those two ranges and then do the math.

If you can not find the info, find a true mil target ( can be found by searching or here Storm Tactical FREE Downloads, Targets, Sniper Rifle, Precision Rifle, Storm Tactical University)

Go to a range and setup for 100Y, at x12 your the mildots on your reticle should match to the circles on the target. Then move the magnification ring to 20 and see where it ends up. I would find a place on the ring where the reading is x2 to make things easier.

At x12 the dots will match up to 1 mil, as you move up in mag the image will become larger to a point where the target image takes up 2 mils. At that point your range will be x2 what you are reading. Mark that on your scope ring. If you scope moves to a lesser amount, you can reduce below x12 and find the 1/2 point.

The math may work out on paper, but it is common with SFP scopes that the true x1 focus is not at the ring setting, but a little above or below.

I've double checked the math, and I believe it is correct... so I offer the following question purely to learn, not to question your response:

As far as I can see, the error induced would be limited to the true mil value not being at the true magnification value, or the true magnification value not being at the marked spot on the ring. Whether the two don't line up, or the mag adjustment doesn't line up correctly.

So... as in all things precision, would it not still be acceptable to use these calculations as a baseline to get pretty close? Then see what kind of variance one gets to correct the calculation to actual values before going to a competition or hunting or later shooting where 100% accuracy is desired?

Asking honestly, because what I describe here is exactly what I would do if in the OP shoes. I'd use the math to start, then verify and correct at the range. I might be wrong... I use FFP scopes to avoid this issue, and hadn't really given it more than a brief though until today.

 

[roggom]

J, your math may be on, but we actually responded at the same time, that is why I edited the response as a reply to OP. Sure the math will get you close, but most scopes are not graduated small enough to use such precise measurements. The NF has mil, 1/2 mil and circles and dots, but in reality its hard enough to hold the dang rifle still to get a reading. The Vortex used to have small markings on the mag ring with X2 etc for such adjustments.

I use a SFP and 9 times out of 10 its at max and I am dialing dope.