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Calculating bullet drop at longer ranges

Discussion in 'Rifle Country' started by AmericanFreeBird, Jan 13, 2003.

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  1. AmericanFreeBird

    AmericanFreeBird Member

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    I have a favorite load that I've worked up, at 100yds, very accurate. I'm shooting a .95" group of five at 100yds without a lot of sophisticated front/rear rests etc. I know my accuracy will improve with better bench rest gear.

    If I shoot some groups at 200yds., can I use the bullet drop difference to calculate drops at longer ranges?

    I only have 200yds available for test shooting and once I'm in the field if I have a shot at 400yds I'll need to know how to approximate the moa for 400 from my 100yd zero. Any advice?
     
  2. echo3mike

    echo3mike Member

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    I started to think about it a little, and the answer is a resounding probably not. I'm sure you could try if you had some other info, but from the drop from 100->200yds, no way. It's not linear: as an example, I've got a .308 168gr HPBT with an MV of 2678, BC of 0.462. The drop from 100 to 200yds is (about) 1.7". The drop from 200 to 300 is (about) 8.4".

    I can think of a couple of guys that MIGHT be able to give you a pretty decent idea just from caliber, bullet weight and MV, but just from what you've got...nope.

    'course, iffin' you were to go out and borrow a chrony, it'll make your life alot easier...unless you wanna just shoot at different ranges. Or if it's a factory load, you can speak with the maunfacturer and get a decent idea of the approxomate MV. You can use that on one of the online ballistics sites to get a decent idea of an amount of come-up. You'll only be in the ball park, but it'll be alot closer than the average SWAG.

    S.
     
  3. Redlg155

    Redlg155 Member

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    I tend to agree with E3M.

    Given that information, more than likely not. There are ballistics programs out there that will calculate the data for you, but even with ballistic programs the data is approximate.

    If precision shooting (sub moa at long range) is your game, then there is no substitute for getting out there and actually shooting from those distances and keeping the data recorded. Even then you can expect variables that may interfere with the perfect shot.

    Good SHooting
    RED
     
  4. Mildot

    Mildot Member

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    Last edited: Jan 14, 2003
  5. hps1

    hps1 Member

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  6. dakotasin

    dakotasin Member

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    there are so many variables... even if you know the bc and mv, that is not enough. the bc will change as the bullet slows down, and you should chrony at the muzzle and at 100 yards. this will give you an actual bc (instead of advertised bc, which may or may not be right), and will let you know what is really going on.

    of course, if you could provide more data about the load and rifle, chances are that somebody else has already done actual work-ups and can get you ballpark...
     
  7. cheygriz

    cheygriz Member

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    Buy a copy, or go to the library and borrow a copy of the Sierra Reloading Manual or the Hornady Reloading Manual.

    The nice people there have already done all of these calculations for you.
     
  8. cratz2

    cratz2 Member

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    Does it change enough to significantly alter the drop at a given distance? Actually, I don't see how it can change much - I assume you are suggesting that the bullet is elongated during the highest velocity period?
     
  9. Cosmoline

    Cosmoline Member

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    I use "Bullet Performance" by Philip Mannes. A few hundred pages of tables detailing drop based on velocity and ballistic coefficient.
     
  10. Freedom in theSkies

    Freedom in theSkies Member

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  11. Art Eatman

    Art Eatman Administrator Staff Member

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    For low-mount scopes and cartridges like the .243 with a 100-grain bullet; those of the .257 Roberts through .30-'06 class--but excepting magnums and centerfire .22s:

    If you sight in for two inches high at 100 yards, you'll be quite close to dead on at 200. Five to seven inches low at 300, and roughly two feet low at 400. (True for a 150-grain '06 for the last half-century. :) )

    Boat-tail bullets can be maybeso two to four inches flatter out at 400.

    Specifics are best treated by the "External Ballistics" section of the Sierra reloading handbook. IMO, it's superior to all others I've seen.

    Art
     
  12. AmericanFreeBird

    AmericanFreeBird Member

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    The load is using a Hornady 155gr Balistic Tip BTHP AMAX .308 bullet. .308 Win with 47.0gr of Hogdon's Varget.

    Now the book lists the expected MV and darned if I can remember it exactly but with a 26" barrel I'm thinking the MV is 3020fps. According to the listed MV, I don't have a crony, yet! :D

    Thanks for the help and the links!
     
  13. Art Eatman

    Art Eatman Administrator Staff Member

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    AFB, you oughta be right on my '06 trajectory...Near as I can tell from the behavior, I'm pushing my 150-grain bullets at 3,000, mas o menos.

    Art
     
  14. JerryM

    JerryM Member

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  15. AmericanFreeBird

    AmericanFreeBird Member

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    That is one cool site, thanks!
     
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