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front focal plane,what is it and how does it work?

Discussion in 'General Firearm Discussion' started by Hardwood floor guy, Mar 31, 2012.

  1. Hardwood floor guy

    Hardwood floor guy Beaverton Active Member

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    So I have a leupold mark4 4.5x14-50 power scope with tmr reticle and i dont think it has the ffp but what is the hype
    about ffp scopes?
    some other forum talk says that it makes ranging quicker but how?
    and my scope without the ffp i have heard goes into the second plane at 10x so how does this effect ranging or adjusting the scope?
     
  2. MarkAd

    MarkAd Port Orchard Well-Known Member

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  3. trevoro

    trevoro Coastal range Member

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    A FFP scope allows you to use the reticle for ranging no matter what magnification the scope is set to. The distance between the marks on your reticle will be the same at 4.5 power as at 14 power with a FFP scope. With a FFP scope, the marks will "shrink" as you go to lower power, though they will remain the same relative to the target. With a SFP scope, the marks will appear the same size as you adjust the magnification.
     
  4. Hardwood floor guy

    Hardwood floor guy Beaverton Active Member

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    good article mark.the one thing it didn't cover though is if you go into the second focal plane at 10x then does a shot your taking at 500 yards have to be under 10x magnification when you range the target?or do you always want to range at maximum magnification
    regardless of distance to the target?
    i understand that with a ffp scope it is a constant rather 100yds or 1000yds but im not sure if i have to be at 5x to range 500 yds or
    14x for all targets.
     
  5. Flopsweat

    Flopsweat Slightly right of center Well-Known Member

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    I'm going to assume that by "goes into the second plane" you mean that 10X is the only setting where mils equal inches. You can use the reticle to estimate the distance to your target if you know the height or width of your target. Then you'll know how much you need to adjust your elevation to compensate for bullet drop. Suppose you are shooting an 8" target. You know that at 100 yards, it will be about 8 mils (the hash marks on your TMR reticle) from top to bottom. Say that the target farther away than that, but you don't know the exact distance. Look at it through the scope with magnification set at 10X. If it's 4 mils high, you know that your target is twice as far away, or 200 yards. Let's say that you sighted your rifle in at 100 yards. You consult your notebook or ballistics program, and determine that the bullet will drop 3" below your point of aim at 200 yards. 3 inches at 200 yards is 1.5 MOA, so you crank in 6 of those 1/4 mil clicks on your elevation knob, and are theoretically now sighted in for 200 yards (I skipped windage to keep it simple). Now you can adjust the magnification to whatever you like and shoot. A good scope will have the same point of aim at all magnification settings. Each time you want to shoot at a different, unknown distance, you need to go back to 10X magnification to measure the apparent size of the target and perform the rest of the steps. With a FFP scope, you can measure the target at any magnification, not just 10X, and still get an accurate estimate of the distance. It saves you having to switch back to 10X to measure the size of your target.

    There is a little more to it than that, but this should help get you started. The spinning of the bullet will also pull it sideways a small amount. This (windage) is also included in ballistics charts, and works the same way as adjusting elevation. With my 223 it's about one click when going from 100 to 200 yards. Also, one MOA (Minute of Angle) is not exactly one inch, but it's close enough that I never worry about it at less than 600 yards, and can't hit much beyond that anyway. ;) Last but not least, I've probably left something out or may have gotten something wrong. If so, rest assured that someone will be along shortly to correct it. :D
     
  6. MarkAd

    MarkAd Port Orchard Well-Known Member

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    i think these will help even more.

    User Guide

    8541 Tactical - Mildot Range Estimation

    "With a FFP scope, you can measure the target at any magnification, not just 10X, and still get an accurate estimate of the distance."
    This is correct. The mil-dot grows and shrinks with the magnification setting.
     
  7. Hardwood floor guy

    Hardwood floor guy Beaverton Active Member

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    there is so much to learn on this scope with the tmr reticle and all that i have had to learn piece by piece.
    I learned my trigonometry for scopes(already knew it as a machinist but learning miliradians)was first,now i have a clear understanding of ranging with the tmr reticle and adjusting the turrets.
    after reading your awesome advise i used the morning to learn about the ffp vs second focal plane and think i have that figured out pretty well so now i can work on windage calculations at different ranges.
    thanks guys for your valuble input.
    when i ranged a 2x4 across the street in 4.5 magnification and it read 222 yards i knew that was off so as i went up in magnification the mils shrunk so i have a second focal plane for sure and it is best to range in full 14x magnification.
    in 14x magnification that same 2x4 was 73 yards so it makes a big difference understanding the ffp vs sfp when ranging.
    the 10x theory i was shown was wrong and only works if you stay in 10x all the time.
    i have a new respect for snipers retaining this knowledge and using it in battle to make quick adjustments in seconds.