Can someone please check my math for me.

Discussion in 'Long Range Scopes and Other Optics' started by crusier_32, Mar 22, 2008.

  1. crusier_32

    crusier_32 Member

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    Hello, this is my first post here. Though I have been reading old threads here for awhile, and have learned allot in the process.

    Anyway I am getting into this long range shooting a bit, mostly with varmints. For the time being I am only shooting a .223, mostly I am just trying to learn the ropes with something affordable to shoot.

    Anyway the scope I am using is a Burris variable 14x with the ballisticplex reticle. For most of what I use it for (inside of 300 yds) I just use the different dots for my hold over, which works fine for the most part. I would like to be able to practice out to 500 hundred though with this rifle. At that range the dots are aways apart and estimating a smidgen high or low gets hard to do.

    But what my theory is though is that I can still use the dots at any range, but then to also turn the knobs so I can place the cross hair right on without any guessing.

    Let me run an example, and if someone could double check me I would appreciate it.

    Lets say I am shooting at 450 yards.
    The drop for the fourth dot on this scope is 29" @ 400yds.
    My drop chart tells me I need to have 8.85 moa of elevation.
    Converting 29" to moa gives me 29/(400/100) = 7.25 moa
    So then I would need to dial my scope up 8.85-7.25 = 1.6 moa.
    Burris uses 1/4" clicks @100 yds so to get clicks 1.6/(1.047/4) = 6.111 clicks.

    Or 6 clicks of elevation using the forth dot on the scope. Does this all sound like a sound theory or am I doing something wrong. I plan on getting out and trying this theory out this weekend. Though I have not tested this drop chart yet, and I try not to change more then one variable at a time here.

    This post got longer then I expected, but I appreciate any insight.

    Thanks,
    Will
     
  2. jwp475

    jwp475 Well-Known Member

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    You state that your scope is a Burris and that they adjust in 1/4" and then you converted to MOA, if your scope adjusts in inches then their is no need to convert to MOA
     

  3. crusier_32

    crusier_32 Member

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    Everything is in inches but. But I don't think I can just add so many inches to whatever dot to get a father range can I. So many inches drop at 400 is going to be different at 450 right? That was my logic for doing it this way.

    Will
     
  4. jwp475

    jwp475 Well-Known Member

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    It is inches per hundred yards (IPHY) raise the impact 2" at 100 yards and this will raise the impact 8" at 400 yards and 9" inches at 450 yards...
     
  5. Eaglet

    Eaglet Well-Known Member

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    Test it at all ranges you plan to shoot. Good luck!
     
    Last edited: Mar 22, 2008
  6. Eaglet

    Eaglet Well-Known Member

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    Crusier_32,​

    [​IMG]

    This is the reticle for my scope, the values are right if the scope zoom is set at 22x. If let's say I need to make a shot at 1050 yards and my drop chart or my PDA says I need 22.2 moa; then I use the bottom hash mark which is already giving me 20 moa and would dial 2.2 moa which would be 9 clicks to be dead on. You could do exactly the same with your scope. The trick is in doing lots of testing to ensure everything is in place.​
     
  7. ss7mm

    ss7mm Writers Guild

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    Eaglet:

    You're gonna love that new scope but one thing you might find when shooting in the field and using the extreme lower hash marks, especially at 22x, is that, although it works and you can do it, it really can make it hard to spot your own shots because the hash mark you're using is in the lower portion of your field of view.

    I'd done it over the years and it works, but I've also found that, at least for me, I prefer to dial for the first shot and use the hash marks to spot my shot if I'm by myself. Usually at long range the time involved in dialing won't be a problem.

    Try it and see what you think but at least for my old eyes I prefer to have as much field of view as possible.;);)

    After you get it mounted and get some time in the field, let me know what you think.:)
     
  8. Eaglet

    Eaglet Well-Known Member

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    ss7mm,​

    I know you have lots of experience with this particular scope and what you're saying is very truthful. I have no doubt I would not be able to do my own spotting.:) Might as well forget it if I was to be by my self. Thanks for the comments I appreciate them.
    We'll let you know.;)
     
  9. Tyler Kemp

    Tyler Kemp SPONSOR

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    What if you sighted that NF in 8 MOA high at 100? You could shoot further without dialing.
     
  10. crusier_32

    crusier_32 Member

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    Thanks for the input guys, I had other plans today but I got confused with all the math so went shooting this afternoon and put some theory to the test. I think me and Eaglet agree with using dialing in more moa on of the hash marks. Though I think if you convert all the hash marks to inches at 100 and then go from that you will arrive at the same conclusion. For me I think I will just figure out where my hash marks are at in moa then divide the difference by .26 get to get my click value. A little extra work, but once I get a spread sheet figured out it won't matter much.

    And oh by the way for my range test I was shooting clay pigeons at 340, on the third hash with 4 clicks elevation. I was shooting in a bit of a cross wind which hurt my windage but my elevation was spot on at that range. Which means this gun is shooting a little flatter then what my drop chart says it should be. I need to borrow a chrono from a buddy though, once I know what my speed is for sure then I will rejigger my chart. Though was awfully cool to see those pigeons go down when you could barely see them with the naked eye.

    Anyway I need to let my brain cool down, thanks for the advice and I will probably be back with a bunch more questions later.

    Will
     
  11. sscoyote

    sscoyote Well-Known Member

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    Another way to do it is to use the reticle itself. If it were me and i had a 450 yd. shot here's how i'd do it. I know that the shot is between the 3rd and 4th stadia @

    3) 7.2 MOA

    4) 10.5 MOA

    ...that means there's 3.3 MOA space between stadia (what i refer to as a "subtension unit"), and 8.85 MOA is 1.65 MOA more than the 3rd stadia (8.85-7.2 = 1.65). So just divide 1.65 by the total "subtension unit" you're working with (3.3) and u get 0.5. Now your hold would be 3.5 (3rd stadia down and .5 further down to the 4th).

    Believe me when i say that an interpolative system of guessing tenths of a subtension unit can be accurately referenced. I've already seen this 1st hand when my wife and my mother used the system for their 425 yd. gps. they shot with an AR by referencing between stadia. It's also the same system that the mil-dot guys use when they're ranging with their reticle.

    Before u use this system tho, it's a good idea to measure the reticle subtensions as accurately as possible. It wouldn't be the 1st time i've seen ballistic reticles that weren't accurate--especially with the advertised plex post tip subtensions. Mine are quite a bit different than advertised.

    What i usually do is use reticle to it's subtension limit, then turret beyond that using the lowest reticle stadia as my zero reference. This usually gives me all the accuracy i need with the reticle then more accurate turret reference beyond that range. Be sure and verify the lowest stadia's zero tho. If that's not accurate then the turrets certainly won't be either.
     
    Last edited: Mar 22, 2008