Rifle Scopes 1st & 2nd Focal plane holdover / windage question

[subseauk]

Hi all
I have what may be a simple question for some of you guys.

I have been offered a S&B PMII 5-25x56 P4L / 2 ( which i assume means 2nd focal plane reticle ) in Milrad turrets.

Now i know to use the the mildot ( hash ladder ) reticle for ranging these scopes in 2FP have to be set at sertain magnification.

My question is once the range is known by milling or laser and the wind value is also known and converted to mils. Does the mil value alter with the magnification setting? ie if the holdover is 1 mil at 5x mag will it still be the same at 20x mag? if not how is the difference adjusted ? is there a formula of some sort?

Answers in idiot speak to start with

much appreciated guys and great forum BTW.

 

[terrydg37]

Re: 1st & 2nd Focal plane holdover / windage question

If it is Second focal plane, you will be limited to using a certain magnification for milling, I dont know what it is for that particular scope, but if it is at say 10x and your hold is 1 mil than it will not be the same if you are on another mag setting. 1 mil at the lowest mag setting will be much larger than 1 mil at the highest.

 

[Redmanss]

Re: 1st & 2nd Focal plane holdover / windage question

If it is a second focal plane scope, then yes the mil values will change. I'm not familiar with the S&B product codes to tell you if the "2" does in fact mean it is SFP. To the best of my knowledge, a SFP 5-25x is a special order only scope.

If it is SFP, you will need to map the reticle at the different magnification settings. Basically by doing that, you can find out at what settings what your multiplication factor will be. Once you map it, mark it for future precision in your settings later. It adds an additional step to your adjustment figures or ranging, and takes training to master but can be done.

All reasons I won't buy SFP, but that's my own preference.

 

[grayghost]

Re: 1st & 2nd Focal plane holdover / windage question

I['m waiting on a vortex pst in sfp and as I was looking through there web site I found directions on how there hash marks change with magnification settings. It would be nice if the other manufacturers would do the same

 

[sandwarrior]

Re: 1st & 2nd Focal plane holdover / windage question

subseauk,

If you think about it you answered your own question:

"Now i know to use the the mildot ( hash ladder ) reticle for ranging these scopes in 2FP have to be set at sertain magnification."

That's because the scope has to be set on that magnification for the mil-dots to give actual mil value. If you change that then while holding over, you've changed their value, in a second focal plane scope, when you change the magnification.

As Redmanss said though, you can counter that by valuing each, or various power settings on your scope. For instance, on your 5-25X scope, suppose the power setting for true mil is 18X. Then @ 9X you should be 2 mil per mildot. And @ 22.5X you should be .875 mil per mildot. Maybe the correlating power is 12.5X? Then @ 25X you would have .5 mil.

If you can take the scope out and look at it, see what the power is and double or half it and see if it works out. You should check to see if the scope sub-tends correctly anyways though. I would imagine an S&B as quality, though, and you not having that problem.

But the short answer is yes it will change with power setting.

 

[subseauk]

Re: 1st & 2nd Focal plane holdover / windage question

Many thanks guys

nicely explained and confirmed pretty much what i had in my mind.

Seems like a PITA in the 2FP ( i have a 1stFP S&B PMII for my .50BMG and that is a nice easy to use and right on the button. Had it hitting a Fig11 ( 1/2 man ) at 1mile just before December using old de-linked 50ammo.

Sounds like this other model ( unless at a real good price ) will be too much work.

Appreciate all the feedaback and will let you know how it goes.

rgds
Kev

 

[sandwarrior]

Re: 1st & 2nd Focal plane holdover / windage question

subseauk,

I guess it depends on what you are going to do with it as to whether I would buy it or not. If it's an S&B 5-25 and you can get a great deal on it, I would.

Where I would differentiate getting one or not is how intense you want to use it. If you do a lot of comps or use it for work as a tool, then FFP is the way to go. If not, it's a little slower but perfectly adequate. The one advantage a 2FP has over a FFP is you can range using magnification. As noted you get different values for different powers of magnification. You just apply those values with a cognizance of what power you are on. You can't do that with FFP. You can still dial up/down the power on an FFP and achieve the same thing though.