Adjusting for Variable Power MIl Dot (SFP Scopes)

[hogester79]

I have a question regarding SFP scopes that I can't seem to find an answer for, perhaps someone can point me in the right direction?

I understand that mil dot scopes that are not FFP will have a certain power that the mil dots are accurate (usually maximum power but model dependent).

If I want to range find, I use the mil dot methods mentioned elsewhere and now at maximum power I can work out all the things I need to accurately hit my target......

What happens if I am not at maximum power? How do I use the mil dots etc? Are they even relevant at non full power and I am basically just left to use my own "hold" over guesses?

Is there a sheet I can use or do I need to range out the different powers so that I have an accurate data sheet for reference?

The biggest problem I have in Australia is due to my location finding a range with the distances I would want to build my own sheet, just don't exist so I am looking at other options that an outright purchase of a FFP scope.

Thanks

 

[phillietimothy]

Re: Adjusting for Variable Power MIl Dot (SFP Scopes)

Hoges,

Your question will get more replies in the riflescope section. Using a SFP 6-24x scope as an example. Assuming the scope mils on the highest power(not always the case). Here are you subtensions at different powers.

at 100 yards
6x-14.4"
12x-7.2"
18x-4.8"
24x-3.6"

As you can see, the relationship is inversely proportional. With some lower quality scopes, milling is only correct on the stated power. You should verify this yourself with a large target and a straight line. For instance - on 24x, mil to mil will be 3.6". On 12x, mil to mil will be 7.2". Hope this helps.

Tim

 

[Eric B.]

Re: Adjusting for Variable Power MIl Dot (SFP Scopes)

Thus the preference for FFP for mil-dot reticles.

My older Burris Black Diamond scope is SFP and mils on the 12X (highest) setting. Someday I'll sell it but it is built like a tank with quite high quality so I hate to part with it.

 

[JoeZ]

Re: Adjusting for Variable Power MIl Dot (SFP Scop

Please correct me if I am wrong.

Take the magnification (power) setting that the mils are true at and divide by the current setting on the scope to find the current subtention for the mils.

Using the above example:
true at 24X divided by current setting of 12X = each "mil" is now worth (subtending) 2 mils.
Or 24 / 12 = 2
also 24 / 6 = 4 (mils each).
24 / 18 = 1.33 each.

A 20X scope:
20 / 16 = 1.25 each
20 / 13 = 1.53 each
20 / 10 = 2 each

Let's say the scope's max magnification is 22 but the mils are true at 20. On max magnification the "mils" are 20 / 22 = .91 mil each.

Of course this works for moa as well.