Trajectory calculator

Discussion in 'General Crossbow Discussion' started by Cossack, Mar 27, 2009.

  1. Cossack

    Cossack Incurable Tinkerer

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  2. BlackBoarDown

    BlackBoarDown Swine population reduction specialist

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    I plugged in my numbers and compaired them to the Hawke BRC .

    The hawke says for 263 FPS and a 20 yard zero the POI @ 40 yrds is -24.299,
    the above link to program says -20.110743 . I don't think it needs to carry it thru that many decimals but it's a big differnece. I have been shooting with the Hawke and it is good for me out to 40 yards. SO I will believe the Hawke . Good link though .
     
  3. ridgehunter

    ridgehunter Active Member

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    Nice chart! I wonder if you could calculate the speed of your arrow by doing the reverse. Charting the drop in your arrow at the different distances and then figuring the math in reverse. I was a math major among other things and so I think of weird things like this. For those that don't have a chronograph and wan't to know a ball park figure about their arrow speed, it might work.

    Uh, You fellows don't shoot 500 yds with your cbows like the antis say:smilielol5:!
     
  4. Cossack

    Cossack Incurable Tinkerer

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    Good point BBD, that's likely due to this program having been developed for Vertical bow arrows. Being longer, they have a higher ballistic coefficient. Therefore, they fly 'flatter' than a shorter stubby crossbow arrow; just like comparable bullets perform.
     
  5. Cossack

    Cossack Incurable Tinkerer

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    "I plugged in my numbers and compaired them to the Hawke BRC ".

    What number did you use for the ED value (Estimated Deterioration value, BBD?
    Equally important, how did you determine it? Did you just use the value in the program (it's for a pellet gun in my vservion.
    Been playing with the Hawke program to compare the two can't figure out how the ED is determined for a crossbow arrow or if it changes with the size fetching or FOC.
     
  6. Cossack

    Cossack Incurable Tinkerer

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    Re Hawke trajectory calculator

    If you just punch in "crossbow" in the presets it gives an aproximate ED value...not the most accurate way to use the program, but it works. One way is to do like Moon said, use your 20yrd crosshair, take one shot at 20yrds from a bench, then another at say 30 yrds using the 20 yrd crosshair and measure the amount of drop. The best method is to use a chron. You can do off the shelf and another reading at 20 yrds and it will work just fine...20 and 30 will be a bit more accurate but you are splitting hairs. Arrow weights can mean very little. I sighted in a Gold tip dead on at 20 yrds, picked up another arrow that weighed 25grs more and it hit 20" high because the spine was heavier. The FOC on an arrow will make a huge diferance...you can have two arrows weigh the same, one with a higher FOC and they will not have the same ED value. You can also have some interesting diferances from bow to bow, so just plugging in the weight or lenght will not give you much in the way of actual accuracy of a given arrow out of a given bow

    Wyvern

    P.S. Scope height (center of scope to center of arrow on the rail) can have an interesting effect at distance as well...
    Reply With Quote
     
  7. Cossack

    Cossack Incurable Tinkerer

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    Hmmm, not that much difference at all. This program says 11.3" at 40 for my Cyclone and Hawke says 11.9". I'm calculating at 355 fps and the program's
    preset ED value of .0638, since I don't know my actual ED. Now to get some bow/chron time and sort it out. We still have a foot of snow on the ground most places...so I won't be loosing any arrows for a while.
     
  8. BlackBoarDown

    BlackBoarDown Swine population reduction specialist

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    I just used the value it gave for "crossbow" .
     

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