Rifle Scopes Mil dot and magnification

[woodland-ghost]

On my scope the mil reticle changes as magnification increases...it has to be on 12x to be the correct size for ranging and actual mil size.

When I run out of elevation on my scope and use hold overs in the reticle would...

24x only be 1/2 a mil
And 6x actually be 2 mil?

Trying to have an accurate way of getting more range without changing anything on the setup.

 

[00bullitt]

I'm thinking you mean your reticle stays constant in proportion to the target? If so, it is a second focal plane reticle (SFP) and your reticle subtensions change as you change magnification.

To calculate that, you need to know your reticle calibrated setting which you say is 12x. Once you know this, you divide your actual magnification in to the calibrated magnification to get the new subtension of your SFP reticle. So yes, you are correct in your simple math.

 

[billyburl2]

Sounds like you have a good plan. But you need to "map" your zoom range. By this, I mean YOU need to verify that mag is really what the manufacture says it is... This is why first focal plane scopes rock!

 

[woodland-ghost]

Details on how to do this? ^^^^

Before yesterday the furthest I had been out to was 600 and that was just one time, normally at 400 yds. Yesterday jumped out to 1180 so almost doubled my previous and this just keeps on getting more addicting

 

[Rhys]

Details on how to do this? ^^^^

Before yesterday the furthest I had been out to was 600 and that was just one time, normally at 400 yds. Yesterday jumped out to 1180 so almost doubled my previous and this just keeps on getting more addicting

Take a piece of poster board and draw a series of sets of lines on it representing different MIL values at a known range, and then place that poster board at the given range and compare to your scope on the coresponding magnification. This will either confirm the magnification values marked on you scope are correct, or where you actually need to adjust your magnification to be correct.

100 yard example:

1.8" - .5 MIL
3.6" - 1 MIL
5.4" - 1.5 MIL
7.2" - 2 MIL

The longer you set these lines up the better chance you have of detecting any error, as the error will increase proportional to the number of mils you are trying to cover. On other words you are going to more readily see an error when measuring 5 Mils than yuo will 1 mil as the error will be 5 times greater.

 

[sscoyote]

Reticle subtension is inversely proportional to magnification in SFP reticles. My 6-18x Nikon mil-dots are setup to mil correctly at 12x, but at 18x they become 12x/18x X 3.6 IPHY= 2.4 IPHY, which is where i use it for windage/rangefinding purposes and it measures correctly at 67% of the 12x subtension.

My Centerpoint 4-16x MD is setup to mil correctly at 10x, and at 16, the subtension becomes 10/16 x 3.6= 2.25 IPHY, and it does measure correctly @ 62.5% of the 10x subtension.

Interestingly, the Nikon 2.5-8x pistol scope BDC reticle on my Browning Buckmark 22 subtends 15 IPHY to the lower post tip @ 8x. Last year we were shooting at a dirt clod at 230 yds. which required 30 MOA to get to that range. We shot 10 shots with 30 MOA cranked into the turret and hit it maybe 3-5x out of 10 shots. We then cranked the optic back to zero and changed the magnification to 4x where the reticle's lower post tip became 30 MOA now, and hit it ~the same number of times for another 10 shots.

The inversely proportional nature of reticle subtension vs. magnification is a fun concept to play with sometimes.