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Thread: Maths!

  1. #1

    Maths!

    Any mathematicians amongst us?

    If I shoot a 40grain round at 1050ftsec-1 at a zero of 70m what would the impact point be of a 32grain round at 1640 ftsec-1 relative to the 40grain zero point?

    Is it just a straight forward rearrangement of the variables or would I be missing something out doing that?

    And before anyone says it, yes I know I need to get out more

  2. #2
    Quote Originally Posted by limulus View Post


    And before anyone says it, yes I know I need to get out more
    thats a fact, contact jcs of the site i believe he has an ap for this on his phone.......

    you both need to get out more.

    personally i would just shoot em both and see ha ha

  3. #3
    A bit of fiddling around with numbers and I reckon a 70yd zero with a projectile at 1050ftsec-1 is equivalent to a zero of about 100yds for a 1640ftsec-1 round, can anyone confirm this is correct?

  4. #4
    It depends on what you actually did whilst 'fiddling around with the numbers'! Post your working and I'll be able to tell you more!

    If that's what you got by putting the new numbers into a ballistics calculator along with ballistic coefficients of the bullets in question then it's probably a good estimate.

    However, if all you have to go on is the numbers you have above then any calculation would have to disregard air resistance and the masses of the bullets would also be irrelevant because acceleration due to gravity is a constant across all masses. It would be a simple "time it takes to get to target" vs "time gravity has to act on bullet" calculation which would likely be quite inaccurate in a real conditions (i.e. in air!).

    Alex

    Edit: here's what I make it in a vacuum - probably quite a long way from reality in air!

    Click image for larger version. 

Name:	2010_08_26_08_48_19.pdf 
Views:	27 
Size:	19.6 KB 
ID:	2457
    Last edited by csl; 26-08-2010 at 07:50.

  5. #5
    Quote Originally Posted by csl View Post
    It depends on what you actually did whilst 'fiddling around with the numbers'! Post your working and I'll be able to tell you more!

    If that's what you got by putting the new numbers into a ballistics calculator along with ballistic coefficients of the bullets in question then it's probably a good estimate.

    However, if all you have to go on is the numbers you have above then any calculation would have to disregard air resistance and the masses of the bullets would also be irrelevant because acceleration due to gravity is a constant across all masses. It would be a simple "time it takes to get to target" vs "time gravity has to act on bullet" calculation which would likely be quite inaccurate in a real conditions (i.e. in air!).

    Alex

    Edit: here's what I make it in a vacuum - probably quite a long way from reality in air!

    Click image for larger version. 

Name:	2010_08_26_08_48_19.pdf 
Views:	27 
Size:	19.6 KB 
ID:	2457
    ALEX have a word mate, there is life out there you know

  6. #6
    I used the most basic method of the following:

    1050/70=15
    1640/70=23
    23/15=1.533
    1.533 x 70=107

    I figured everything else would pretty much cancel out so just used the respective ratio of speed v distance. In practice it seems to be quite accurate.
    Last edited by limulus; 26-08-2010 at 08:30.

  7. #7
    Quote Originally Posted by centralbeltstalker View Post
    ALEX have a word mate, there is life out there you know
    There is?



    Quote Originally Posted by limulus View Post
    I used the most basic method of the following:

    1050/70=15
    1640/70=23
    23/15=1.533
    1.533 x 70=107

    I figured everything else would pretty much cancel out so just used the respective ratio of speed v distance. In practice it seems to be quite accurate.
    Mathematically it doesn't cancel out at all, because both range and air resistance are proportional to the square of the velocity, whereas your approximation assumes it's directly proportional. I think it's more a case of luck in this case , but it would be interesting to see how it compares across a range of different speeds compared with a ballistics calculator!

  8. #8
    Quote Originally Posted by limulus View Post
    Any mathematicians amongst us?

    If I shoot a 40grain round at 1050ftsec-1 at a zero of 70m what would the impact point be of a 32grain round at 1640 ftsec-1 relative to the 40grain zero point?

    Is it just a straight forward rearrangement of the variables or would I be missing something out doing that?

    And before anyone says it, yes I know I need to get out more
    I'm assuming you're talking .22LR? Go to CCI's website and compare the ballistics of the Stinger and Sub Sonic rounds they make. You can determine (roughly) the things you want.

    Otherwise, Get the ballistic coefficient of each bullet and I can plot it for you easily. Without the BC, it won't happen. In a 22LR when switching from subs to hyper ammo the elevation is easily adjusted for but there is often a windage shift that makes compensation a little more dificult.

  9. #9
    There is this web page which may help, you need the BC as Muir says
    http://www.handloads.com/calc/index.html

  10. #10
    Muir,
    I'm using .22lr CCI subs at 40grain, 1050fps and CCI Stingers at 32 grain 1640fps.
    None of the software Ive seen will predict a poi from a change in variables from one weight/speed combo to another.

    Maybe I have just been lucky with the math vs actual outcome on this occasion.

    Now its a question of 'go out with the long haired one' or spend the evening with excel wrangling with numbers.....hmmm...drinkies wins

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