Are my numbers right?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by Matt27, Jan 1, 2005.

  1. Matt27

    Matt27 Well-Known Member

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    Finally the cattle are out of the pasture and i can tend to shooting my 338 Lapua. Went out last weekend to get some yardages with my GPS to see how far i can get. I can get 1 mile(+,-). With my setup for my rifle i am 19" high at 100yards. Ran the numbers in Sierra Infinity and came up with about 850yard zero. I had a chance yesterday to load a few rounds with charges and shoot through the chrony to get some speeds and see how hot i can go before to much pressure. There is a tall rock formation at 1400yards(+,-) that i set up on. Ran some numbers for 300gr. bullet at 2850(as that is my target goal), cranked in 22min. of elevation and 2min. of left. Zero wind. I haven't had these kind of conditions in a LONNNNGGGG time.

    So my question is ...

    I was roughly .5mil down from point of aim and 1 mil right.

    I have a nightforce 8x32x56 NXS. I was shooting on 16x
    For correct mil ranging it should be on 32x.

    For 16x 1 mil equals (roughly) 7.2" at 100. So at 1400 yards it is 100.8"(roughly)

    1moa at 100yards is 1.047" and at 1400yards it is 14.658"

    So on my rough calculations i should dial in 3.5moa up and 6.8moa left. Am i doing the math right?

    We are suppose to have another day like today tomorrow. 40 degrees no wind and sun shinin. I am going to load 5 rounds of each charge that are safe and shoot at my steel target at 1400 yards. I know, why are you testing at 1400 and not closer? Well i haven't had days like these and i want to take advantage of them and see how they shoot way out there and then i can fine tune the load tomorrow to try and tighten the group up while i have the conditions good. Hopefully i can remember to take my (crappy) digital camera along and photo each group so i can post them to have you guys give me your input.
    This will be the first attempt at 1400yards and my target is 4'x4'. With conditions like they are i hope i can find a load that will do 2moa or less. I think if i can find a load that will do that i will be tickled and can look forward to shooting more and fine tuning it.

    I haven't had the time to work with this gun like my Rem. 260. So now that hunting season is over i am devoting my time to the Lapua and finding the load. I already know my load for the 260 and might try to shoot it to 1400yards and see what it does in these conditions.

    Thanks
    Matt
     
  2. Dave King

    Dave King Well-Known Member

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    You confused me for a while!


    I take it your scope is calibrated for 1 MIL per "mil" mark at 32x.

    At 16x one "mil" mark is 2 MIL. (You'll need to calibrate at 16x to be sure.)

    If you are .5 "mil mark" low ---- at 16x you're 1 mil low (3.44 ~3.5 MOA). Seems you got the math correct if I'm following you.

    Same for windage at 16x... 1 "mil mark" is 2 MIL so you're (6.88) ~7 MOA off in wind.

    Good luck and keep up posted.
     
  3. Matt27

    Matt27 Well-Known Member

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    Thanks Dave

    Sorry about that. Sometimes(alot) i don't type exactly whats in my head. My thoughts get going to fast.
    I was doing the mils all at 100yards in my head.

    32x=1mil(3.6")at 100yards
    16x=1mil(7.2")at 100yards

    As far as my numbers i came up with this is how i did it.

    1 moa at 1400yards is 1.047x14=14.658"
    1 mil at 1400yards is 7.2x14=100.8"

    For the correction of elevation at 1400 i took 100.8"/2=50.4".

    I then divided 50.4"/14.658(Moa)which gave me 3.5moa up

    For the correction of windage i took 1 mil 100.8/14.658(Moa) which gave me 6.8moa left correction.

    I just want to see what kinda groups i can get and if the results are promising i will calibrate my scope for click values so i can do some more thorough shooting to get how many clicks it takes from my zero. After testing this weekend i will find what my Zero yardage is for sure.

    Thanks
    Matt
     
  4. Paul Wyatt

    Paul Wyatt Well-Known Member

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    Sep 26, 2004
    Matt;
    You may want to go to US Optics web site and read what they have to say about the sight plane location of the reticle. Their literature claims that any reticle located in the second plane (NightForce scopes have second plane reticles) will have sighting errors that are introduced at different power settings - in other words they are only accurate at one power setting. Reticles located in the first plane do not experience the same problems. FWIW
     
  5. Dave King

    Dave King Well-Known Member

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    Matt27

    No problem.

    Let me explain better too... to try to eliminate confusion when talking to other shooters.

    A mil (milliradian) is a unit of measure, it can't change based on the scope power setting.

    Your scope is calibrated (I assume) at 32x so that the subtend distance between 2 marks on the reticle correspond to 1 mil.

    As soon as you change the power setting you can no longer refer to the distance subtended between 2 marks as 1 mil (it mearly becomes "marks" on a reticle)...it becomes some other mil value.

    By changing the power to 16x we will assume that the distance subtended between 2 marks is 2 mils. You'll need to verify this with a calibrated/striped pole to be exact.

    In a perfect world if your scope could change power to 8x you'd have 4 mils between "marks".

    So, at 16 power when your round struck .5 "of a mark" low and 1 "mark" to the side it was 1 mil low and 2 mil to the side.

    1 mil is ~3.44 MOA as you note.

    I believe if you think of it in this manner you may find it quicker to make the come-up ands windage correction(s).