Nightforce NXS- Kenton Industries BDC Military spec turret.

Discussion in 'Long Range Scopes and Other Optics' started by Down Under Hunter, Feb 24, 2009.

  1. Down Under Hunter

    Down Under Hunter Well-Known Member

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    I am looking at getting Kenton industries to make a BDC sleeve for my NXS to simplify shots out to around 600 M with little or no windage corrections needed. In theory I am getting alot of my shots present at distance out to around 700 yards and I am looking at using their mil spec sleeve that has the std 10 moa quarter clicks in the std position plus 3 tiers of distances for 30 minutes of elevation from my zero. Obvioulsy this does not help at all with windage adjustments.

    I am well aware of the downfalls of the BDC design, loads, conditons changing, downdrafts, updrafts etc. Also I am smart enough to know it aint as simple as dial the range and aim dead on.

    I am lead to believe however at these medium ranges within a certain range, BP changes, temp , RH will only have small effect out to a certain distance.

    QUESTION 1- What is the maximum effective range you feel this technique can work to accurately with high percentage ?

    Question 2- My understanding is the largest conditon to contribute to POI change is Baro STN pressure. The lowest number I have shot a is 27.8 and the highest is around high 29's. With the most coming between 28.5 and 29.3. Where do I pick the most effective figure to use ? And what sort of impact change at 700 am I going to find between the above BP's when used for elevation dope ?


    Question 3- Can you see a major flaw in my thiinking ? I know dialing is the way to go, but for some of these chances I get where I am time poor and need to set up and shoot at a medium range , I can see some merit in the BDC. I also have the ability to exbal and dial for the long ones because I have the std 10 moa clicks on the bottom to use ?

    I am shooting a 338 Edge 2834 fps 300 smk temps at 50-80 deg, BPs between 28.5- 29.3 AV
    [​IMG]


    How does this sound ?

    DUH
     
    Last edited: Feb 24, 2009
  2. trueblue

    trueblue Well-Known Member

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    I think the concept is sound. However, I would limit the distance to 500 yards or less. I have experienced 1/4 click differences in dial up at 700 yards with minor changes in BP. This would cause a complete miss on a 8-10" target. I am interested to see what others with more experience say on this.
     

  3. Len Backus

    Len Backus Administrator Staff Member

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    Does this help? This shows the max change in MOA within the conditions mentioned. I am not sure if .768 is the agreed upon BC.

    [​IMG]
     
  4. Buffalobob

    Buffalobob Writers Guild

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    There are two principle adjustments to make to a BDC knob once it is "engraved".

    In the world of air pollution control and smoke stack design is a set of peculiarities known collectively as the adiabatic lapse rate. Put simply, the higher up you go the thinner the air and the colder it is. So as you increase your altitude the bullet will strike higher from less dense air if the temperature is the same. But colder temperature makes air denser so the bullet will strike lower at a given altitude if it is colder.

    So here is one example of what I include at the top and or bottom of all of my drop charts for my particular rifle and for my particular bullet.

    What you see is that the drop table was run in the computer with a setting or 5175 feet of altitude and a temperature of 60 degree Fahrenheit. I then change the temperature by 10 degrees while holding the altitude constant and determine how much that affected the bullet strike at 1000 yards and make a note that it affects the bullet strike by one inch or a change in the dial of 0.1 inch/MOA. Then I reset the temperature back to original setting and change the altitude by 1000 feet and check to see how the bullet strike is at 1000 yards and record that as a change in drop which is 0.2 inches/MOA.

    Those two factors can be ratioed by distance if you wish such that at 500 yards the factors would be half and at 2000 yards the factors would be doubled. Also if you are expecting 60 degree temperature but it is 30 degrees colder then multiply by three. Ratioing will not be extremely precise due to the nature of ballistics but if you stay withing reasonable distances and changes it will be fine because the adjustments are small.

    You must keep track of positive versus negative change because under normal situations temperature will be subtracted from altitude. Also things change during the day.

    In summary temperature and altitude are the two principle factors and you should determine them for you bullet and your hunting area. Only you know the range of extremes you can expect to encounter.

    The process might even work if you use meters and centigrade. :D
     
    Last edited: Feb 24, 2009
  5. CS T

    CS T Official LRH Sponsor

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    For BDC know I tend to recommend getting a generic BDC knob because even if you get a custom one for your rifle it tends to only be good for that altitude & temperature to be spot on. I look at a BDC knob as a quick guide to the distance I need to dial in. I have used the Kenton BDC turrets myself and they work nicely.

    We stock the 300win mag., 223, and 308.

    Mike @ CSGW
     
  6. Down Under Hunter

    Down Under Hunter Well-Known Member

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    Many thanks all. I'll think I will just keep dialliing by the sound of it ?

    DUH
     
  7. Kenton Industries

    Kenton Industries Member

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    I'll be happy to help you out Down Under Hunter

    For your field conditions lets take the two extremes of BP and temp.
    Your bullets BC is .770 at the velocity of 2800 fps. Zero range at 200yrds

    MOA 500yd 700yd 1000yd
    Case 1: 50F at 28.5 in Hg 7.1, 14.6, 23.5
    Case 2 80F at 28.5 in Hg 7.0, 14.3, 22.9
    Case 3: 50F at 29.3 in Hg 7.2, 14.7, 23.8
    Case 4: 80F at 29.3 in Hg 7.1, 14.4, 23.2

    spread in temps at const BP = 0.6MOA @ 1000yrds
    spread in BP at const temp = 0.3MOA @ 1000yrds



    e-mail info@kentonindustries at I'll be happy to discuss this further.

    Very Kind Regards;

    Mark Kenton
    President Kenton Industries
    530 New Los Angeles Ave. Suite 115
    Moorpark, Ca 93021
     
    Last edited: Apr 30, 2009
  8. petenz

    petenz Well-Known Member

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    I'd use them out to 500 yards or so, but I'd just make my own...
     
  9. MontanaRifleman

    MontanaRifleman Well-Known Member

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    DUH, this may sound a little flippant.... but why dont you just memorize your drops out to 700 yds and have a couple of quick reference charts to go to for various altitudes/pressures.

    1" of Bar pressure = about 1000' elevation (close enough for government work to 700 yds).

    Runnig your ballistics at 1000' and 2000' elevation, I see only 1" differenc in drop... both 12 MOA (48 clicks), at 600 yds - 9 MOA, at 500 yds - 6 1/4 MOA, at 400 yds - a chip shot holding cross hairs just above the back.

    Beyond 700 yds.... well.... you might wanna just take the time to nail it down right and if it's too long... oh well :)

    Cheers,

    MR
     
  10. Down Under Hunter

    Down Under Hunter Well-Known Member

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    At the moment I have a Leupy turret strapped on with retractable tape. Seems to be working but I like the neatness of one less turret.

    Multiple ways to skin a rabbit I guess !

    DUH
     
  11. Sharpstick

    Sharpstick Active Member

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    I use a yardage marked turret out to 1000 pretty regularly. As someone noted earlier, generally when I'm a couple thousand feet above the alt my dial is set for, the temp is lower so the change in POI isn't much. I have 3 that cover me from sea level to about 11,000. I do have a chart for my hunt, but it rarely leaves the pack. When I do have a situation (incline, environmental) that would make my dial off a decent amount, it's just as easy to reference the chart and add or take away a few clicks as it was when I used MOA dials. For 80% (maybe 90%) of my hunting shots, I dial and shoot. The speed of a yardage marked turret makes it well worth the only drawback I have found, which is buying an extra dial or 2 if you hunt places with a big alt change.

    Mine are specific to my load and rifle. For hunting, most of my shots are under 600. At 600 yards my sea level dial groups around 5" low when I'm at 7000'. If I'm within 3000' & 30 degrees of what my dial is set for, and it's less than a 20deg incline, I don't even think about manually compensating if it's 1000 or under. That covers almost every opportunity I have.
     
    Last edited: May 2, 2009