Vari-range scopes and Mil-Dot;

[JoeF]

Ok; so I'm getting in to long range, and everything makes sense except for 1 question:

1.) My scope is a 6-24x44 with Mil-Dots. I understand that I mil is 3.6in at 100yds and 36in/yd, but at what setting do you use on the scope to get that? Is there a "standard" setting like 6x or 10x or whatever?

regards,
JoeF

 

[KRP]

There is probably a mark on the magnification ring showing where it is calibrated, if not it should tell you in the manual. If it is FFP it doesn't matter.

 

[JoeF]

thar was quick. thanks.
next question, whats ffp?

 

[ICANHITHIMMAN]

First focal plane

Whats the optic? I can most likely tell you off the top of my head what focal plane it is. Chance are you have a second focal plan optic, which means that all your adjustment need to be (for simplicity) made at the highest magnification setting on your optic to make these adjustments. Due to the fact that when you turn up or down the power the rectical actualy changes size in relation to your target. Meaning if you are zeroed at 300m and 10x and then you dialed to 4x, and you make an adjustment to your optic it will not be the same adjustment as it would have been if you where on 10x when you dialed. So unless your a human calculator (I'm borderline special) all adjustments need to be made at max power. Then adjusted for if you dial down the power.

If you optic is a FFP model then the magnification setting is not a factor in you adjustment range, as the size of the rectical does not change in relation to your target. The values are the values.

I think I got that feel free to pic out any incorrect data guys as I only do the FFP thing.

 

[DocB]

Roger That!+1

Simply put, FFP - First Focal Plan and SFP - Second Focal Plane refer to the location of the lens that contains the reticle within the scope itself. Like stated, a First Focal Plane reticle will 'grow bigger' or smaller as magnification is increased or decreased, allowing all of the reference points on the reticle to remain in the same relationship to what you are viewing regardless of the magnification. The distance/mil relationship at 5.5x is the same as 20x, 1 mil reticle distance is still 1 mil. That's because of where the reticle is located within the scope, in the first focal plane, near the primary objective.

Ok, now a SFP reticle is located closer to the viewing optic and because of this, it will not 'grow bigger' but will remain the same size regardless of magnification. So the mil values will change proportionally with the magnification. Your scope will have a 'reference' or 'base' power, maybe two, where 1 mil will equal 1 mil, or 3.6" at 100yds. If you increase or decrease power, these values will change not the reticle. Say, if your base is 20x and you are viewing an object and it measures 4mils then at 10x and it measures 2 mils, the reticle doesn't change, the object 'size' does, so it's now 1/2 the size as before, so 1 mil value now equals 2 mils.

Having used both, I prefer a FFP. I range a lot with my reticle, a modified Gen ll Mil Dot with Mil/Mil adjustments, so it's quick and easy, no math. Just one formula if I'm not using my Strelok, " Ht. in inches x 27.77 / mils = range". The Mil-Dot Master is a kewl tool also. With practice you'll know basic ht.s of your targets like second nature. Zeroing is easier also. Holds and dial ups are faster and more intuitive. If you use one load regularly, range cards are a breeze to make for mil holds.

It's pretty much personal preference and how you intend to shoot. But it's like one of our compadres said on here ... don't matter what you use, as long as you hit it and it drops in it's tracks..it works!

Personal note, I would like to thank all the 'ole timers' on here for taking the time to school us less skilled and experienced. I can't tell you how much I've learned from you guys by just going thru the archives and articles. So many are the times that a conundrum has just unraveled in my research and reading of your threads. lightbulb Thanks guys for taking the time to help us out!

Your humble padiwan long range jedi!

Docgun)

 

[JoeF]

I am currently using a TruGlo 6-24x44. Just learning the mil-dot ranging thing, and I hit the targets at the known distances, so it's not moving. Should be good enough to learn with. From the reading I just did; I think it would be in the FFP type of scopes, so that would mean I need to be at max mag; correct?

I also want to thank you for the replies. I've got to let this sink in for a day or so, then I'll be back with more questions, trust me.

Thanks again.

 

[KRP]

If it is FFP it doesn't matter what the magnification setting is, reticle subtension remains the same.

 

[sscoyote]

Joe, I doubt that optic has the reticle in the FFP, it's probably in the SFP, as most of the less expensive optics are, and i doubt the mil-dot is setup for 24x, since most higher-powered scopes aren't set up that way. Most are at a lower power. Is there not some sort of indicator on the power ring somewhere? Most are setup to let folks know what power the optic must be on to mil-range correctly. Most are setup for 10, 12 or 14x, although there are a few exceptions to all these "mosts".

I'm going to assume that you have a SFP optic, so to understand the concept of why it must be on the correct power to range with, look through a window of your house at something outside...DISCREETLY and SAFELY of course. While keeping the center x-hair on some point adjust the power up and down, and you will see that the mil-dots move up and down on the target as you change power. This is why the optic must be set on the correct power so the distance between dots measures (subtends) 3.6" at 100 yds.

I think somebody mentioned above that the quality of reticle subtension changing with magnification is actually inversely proportional, because as you INCREASE magnification you DECREASE reticle subtension. Think about that concept as you change the power. For instance, if that optic is setup for 12x, at 24x (2x the magnification) it'll be about 1/2 of 3.6" at 100 yds. or 1.8".

BTW, welcome to the world of subtension vs. long-range shooting and rangefinding. It's one of the most intriguing and rewarding aspects of the shooting sports.

Oh and BTWx2, you should know how to say and spell subtension, as it may impress other shooters, and they will probably think you know something about shooting--it's worked for me.