Scope adjustment question

Discussion in 'Long Range Scopes and Other Optics' started by Water Swatter, Feb 19, 2008.

  1. Water Swatter

    Water Swatter Member

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    Feb 12, 2008
    I just recently joined the site, great information, great site.

    I just recently bought Sierra's infinity software. I am looking at trajectory charts and I am wondering about adjustments for point of impact. For example I ran a chart for a 140gr Nosler Accubond with a 400 yard zero, the software tells me with a 400 yard zero it would be 4.66" high at 100 yards.

    Assuming my gun was zeroed at 100 yards would I need to adjust the turret for basically 4.6" up to be right on at 400, removing all other external factors. It seems to simple, the math I mean not the shot, it seems like I am missing something.

    The same for 500 yards, @ 100 yards it shows 6.59" high, so by the same logic in a perfect atmosphere if zeroed at 100 yards the correction for that distance would be 6.59" to be dead on at 500 yards.

    This is assuming the scope has the room for adjustment.

    Am I missing something or is this the correct way to start building charts for a specific load?

    ws
     
  2. woods

    woods Well-Known Member

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    Jun 4, 2006
    As long as you are talking about moving that 4.6" or 6.59" on the 100 yard target you are correct. You are just moving the POI up and down.
     

  3. britz

    britz Well-Known Member

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    Mar 11, 2007
    Welcome aboard!

    The thing about balistic software is that they are never "perfect" They will get you very close (I should say that they information that you have to enter isn't always right on the spot). Some bullet manufactures list inacurat BC's for their bullets and tradjectory at different altitudes vary. Also, Your actual velocity may be very different from what is listed for the load you are shooting. If possible you should test them with a Chrony. You should always test your load on the range at the distances that you intend to shoot at to correct the differences between what your program spit out and what your bullet actually does. I am not familiar with that program - I just use JBM calc on the net.
     
  4. Water Swatter

    Water Swatter Member

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    Feb 12, 2008
    Based on a 100 yard zero the chart shows the bullet 18.63" low at 400 yards, then changing the chart to a 400 yard zero it shows 4.6" high at 100 yards, I am making the assumption that his would be the adjustmentbe dead on at 400, in a perfect world.

    I understand that this is based in a perfect world and nothing is for shure until I get to the range and varify, but this is just a starting point for me.

    ws
     
  5. HoytemanPA

    HoytemanPA Well-Known Member

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    Dec 16, 2001
    You have it right. Shoot a 7mag?

    Successful drop charts depend on your scope. If your scope adjusts in inches/100 yd, you will want to just use the inches provided on your program. If it adjusts in MOA the number calculated gets divided by 1.0472.
    If it adjusts some weird number it gets divided by that.

    However once you start doing it, it won't take long and you will forget the 4.66 and the 6.59 stuff and know 400 = 4.5, 500 = 6.5, 1000 = 23. etc.

    I use the divisor of 1.05 (MOA) in my calculations as my Leupold LRT's are very close to that. I shoot a group at 100, dial the scope up 20 numbers and shoot another one. I come up with 21 inches.

    If I had came up with 20, my divisor would have been 1.00 for the rifle.

    Likewise if I came up with 19, my divisor would be 0.95. Bottom line, match your chart to your scope. And try and adjust the available inputs to closely align your calculated data with your real world results.

    Shooting elevated groups also gives you the indication of how well your scope is leveled at the same time. (Provided you drew a vertical line with a level and you are sure your rifle is level.)

    Good luck,
    Shummy
     
  6. 30-338

    30-338 Well-Known Member

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    Jan 25, 2008
    Sierra Software


    WS...I have the Sierra Infinity V ( I have not purchased the new version yet) but assuming there are no major changes, I think you are slightly confusing 2 issues...1) inches high under bullet path column at 100 yards and 2) elevation correction for a given range. As far as I can tell your math is good, but the software will do all this for you. You should have 10 columns on your calculated page , NOT 8...If you have 8 columns then go to the "Trajectory" column and click on "dual MOA" ...accept values and then calculate and you will end up with 3 separate columns relating to "Drop" they are "drop in inches" "bullet path in inches" and "bullet path in MOA". The two relevant columns are bullet path in inches and bullet path in MOA

    The sequence is... you decide on your zero based upon what kind of hunting or shooting you anticipate doing. (The bullet path in inches will tell you how high the bullet is above POA at any intermediate range...also, play around with the PBR functions under the "Operations" column) Then sight your rifle in at this range using the "bullet drop in inches" column, noting how high the bullet is at 100 yards ( if you are sighting in at 100 yards) and get you rifle to group as closely as you can to this figure (i.e. "x" inches high at 100 yards). There is flexibility here e.g. One of my scopes has elevation correction of 1/2 MOA so sometimes I cannot get to the exact point due to 1/2 minute clicks...but the software can help with this also. You can enter various zeros in the "Zero Range" box and fine tune your chart, ending up with a very close correspondence to the inches high at 100 in the bullet path column and your group on the target. I sometimes end up with zeros of 227 yards or 243 yards or whatever and it makes no diference if you end up with an odd number for your zero.

    Then print your chart making sure you have 10 columns . You will then be able to look at a distance to target...and move your finger over to the bullet drop in MOA column ...dial the necessary correction and shoot.

    All the other members have given excellent advice...you absolutely must chrono loads, and HoytemanPA has given a very cool way of seeing exactly what your scope does with each click...thanks Shummy! That helped me!

    And you are right, this is a starting point. But you can fine tune in the real world. But the software is, in many cases remarkably accurate, and helps save time. Good Shootin' 30-338
     
    Last edited: Feb 20, 2008
  7. Water Swatter

    Water Swatter Member

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    Feb 12, 2008
    .300 Win Mag
    Nikon Buckmaster 1/8" adjustments, or was, I am in the market for a new better quality scope. Looking at the Nikon Monarch or Elite 4200.

    What is the difference between 1/4" adjustment and 1/4 MOA adjustment? The MOA adjustments are confusing, where can I read up on these adjustments? MOA language is foreign to me, (If it adjusts in MOA the number calculated gets divided by 1.0472), what number gets calculated?

    I use a Wheeler level, level, level to level my scope when mounting a new scope. Is there a beter way then that? It seems fine out to 300 yards but I have not been adjusting the turrets before now

    Thanks again for the information.

    ws
     
  8. Water Swatter

    Water Swatter Member

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    Great advice thanks.

    ws
     
  9. spdcrazy

    spdcrazy Well-Known Member

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    Feb 18, 2008
    i'm new to this whole thing as well. but from what i have read so far, some scopes have different definitions of MOA. some ppl use 1" @ 100 yds for MOA. but the precise definition for MOA is 1.0472" @ 100 yds. doesn't seem like much when your shooting at 100 yds. but at greater distances it could mean a kill or no kill. there is some good reads on this site about MOA. i just read them yesterday, but i don't remember where they are. i'll look for them in a min. hyotemanPA was trying to say that if your told that you will be, lets say, 14.3 in. high at 100 yds to shoot dead on at 600., you need to adjust your scope down 'X' number of clicks. but you need to know if your scope is adjusted for true MOA or 1" @ 100yds or some other random factor. than divide the 14.3 by MOA (1.0472) or 1" or the other random factor. that will tell you how many clicks to adjust your scope. the numbers i picked were completely random FYI.
    hope that is all accurate and don't thank me if it is. the credit goes to hyotemanPA and this site for teaching me about it on my vacation days off work!