Cosine or degrees which do you prefer?

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by JAWZ, Nov 18, 2009.

  1. JAWZ

    JAWZ Well-Known Member

    Messages:
    187
    Joined:
    May 2, 2008
    I have both a cosine indicator and a degree indicator which 1 do you prefer to use or find easier.
     
  2. BryanLitz

    BryanLitz <b>Official LRH Sponsor</b>

    Messages:
    633
    Joined:
    Mar 8, 2007
    It depends on what method you use to correct for the angle.

    If you use a ballistics program that accepts degrees as an input, naturally you want the device to measure degrees.

    However, if you're using range cards, the cosine is more convenient because you just multiply the drop by the cosine.

    Consider how you're going to use the 'look-angle' information, and that will tell you how you need it indicated.

    -Bryan
     

  3. JAWZ

    JAWZ Well-Known Member

    Messages:
    187
    Joined:
    May 2, 2008
    I use exbal but if it was to shut down or battery go flat it sounds like my cosine 1 would be easier to use with the range card back up.
     
  4. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,269
    Joined:
    Aug 10, 2003
    Bryan, don't you mean Drop*[1-COS(@)]
    If you would have 100" drop level, but shooting at 30deg,, 100*COS(30deg) would appear to be 15.4"
    Where 100"*[1-COS(30)] would be 84.6" (I believe this).
     
  5. royinidaho

    royinidaho Writers Guild

    Messages:
    8,853
    Joined:
    Jan 20, 2004
    Some one ought to check with Shawn Carlock and or Buffalobob regarding this thread. There was a thread on this subject several years ago but I've had know luck finding it.

    The key seems to be where to insert the cosine into the eq'n..........
     
  6. BryanLitz

    BryanLitz <b>Official LRH Sponsor</b>

    Messages:
    633
    Joined:
    Mar 8, 2007
    Mike,
    I think you have COS confused with SIN (or degrees confused with Radians).

    COS of zero degrees is 1.0 [cos(0) = 1] so if the look angle is zero degrees, you multiply the drop by 1.0 (no change).

    If the look angle is 30 degrees, COS(30) = 0.87; so you would multiply the drop by .87.

    If we applied your equation (drop*[1-cos(@)]), the drop would be zero for all level shots: drop*[1-1].

    I'm pretty sure you multiply the drop by the COS (cosine) of the look angle.

    -Bryan
     
  7. Mikecr

    Mikecr Well-Known Member

    Messages:
    4,269
    Joined:
    Aug 10, 2003
    My Bad.
    My ACIs are in degrees, and I tend to think about it as I'm used to seeing it.
    I enter degrees into a ballistic spreadsheet, that corrects PATH.
    Basically adding DROP*(1-COS(@*PI()/180))
    I'm taking care of the Deg/Radian part there..

    But the Cosine ACIs pretty much take it to 'percent of' as indicated.
    So there would not even be 30degs indicated with these, for that angle.
    It's cleaner

    My appologies to the poster, and Bryan thanks for the correction.
     
    Last edited: Nov 19, 2009
  8. 7mmRHB

    7mmRHB Well-Known Member

    Messages:
    338
    Joined:
    Jan 12, 2005
    Using the degree of angle is far more accurate than COS !! Here is an example from my Ebal charts for my 7mmRHB fireforming loads.

    168 berger @ 3255 fps-- starting 3" high at 100yds, takes 16 min. IPHY elevation change at 1000yds. Shooting at a 30* angle the COS tells you 87% or 870 yds shot equivalent ( 12 min.IPHY)

    Now going to Exbal and hitting the angle shooting function on ECCEL and looking at the chart for a 1000yd shot at 30* and it gives you 14.25 min. IPHY or the equivalent of 925 yds to make the shot !! This is because you still need to take into account the time of flight and the effects of air drag on the bullet for the entire distance ( 1000yds )----RHB
     
  9. BryanLitz

    BryanLitz <b>Official LRH Sponsor</b>

    Messages:
    633
    Joined:
    Mar 8, 2007
    RHB,

    Multiplying the range by the cosine provides a very rough estimate. However, if you multiply the bullet drop by the cosine, it provides a much closer estimate.

    Ultimately calculating a trajectory with degrees is the most accurate way, but the estimate provided by multiplying drop by the cosine is quite close.

    As an example, consider a typical trajectory that's -314.3" low at 1000 yards for a level fire scenario. Incline the trajectory by 30 degrees, and the drop is now -271.4". If you approximate the drop by: -314.3" * cos(30) the answer is -272.2", which is only 0.6" different than the direct calculation.

    -Bryan
     
  10. 7mmRHB

    7mmRHB Well-Known Member

    Messages:
    338
    Joined:
    Jan 12, 2005
    You're absolutely correct Bryan. I guess I should have read your posts more closely. We have discussed this subject many times on LRH so when I saw ACI my brain just jumped ahead of what was being said. My mistake. However, I still prefer to use an angle chart and not have to do math in the field. Since my range finder gives me the degree of angle, I find it much more simple to use the Exbal angle chart ( unless Groupers there with his PDA )to make my shots!---- RHB
     
  11. theodore

    theodore Well-Known Member

    Messages:
    293
    Joined:
    Feb 9, 2009
    Why not both?
     
  12. Bravo 4

    Bravo 4 Well-Known Member

    Messages:
    1,995
    Joined:
    Jul 20, 2007
    Why not both...what? Do you mean to have a tool that gives both readings?

    As for the original post, I prefer a cosine reading. That way I don't have to carry a conversion chart, need to convert that angle into a decimal. The only reason I can see needing degrees is that your ballistics program only allows you to use degrees. I use JBM at the house and I believe it will only let you inpute degrees. I can use cosine with exbal. If exbal goes down in the field I would multiply my drop for a given range (Improved Rifleman Method) by the cosine to get the corrected for gravity drop. The ballistic programs are supposed to be the most accurate due to effects of time of flight and such.
     
  13. theodore

    theodore Well-Known Member

    Messages:
    293
    Joined:
    Feb 9, 2009
    Yes, Horus Vision have ASLI (Angle Slope Level Indicator) reads both cosine and degrees.
     
  14. bigbuck

    bigbuck Well-Known Member

    Messages:
    1,650
    Joined:
    Jun 20, 2009
    You can see it at WWW.MountsPlus.com