7.62x39R ballistics info

Discussion in 'General Rifle Discussion' started by SoL, Mar 29, 2010.

  1. SoL

    SoL New Member

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    hi there

    Got a cheap large load of milsurp 7.62x39r for my bolt action.
    What is this calibre decently flat out to?
    I'm thinking of zeroing it for about 100metres, most game we see is less than that due to dense scrub.

    Will that be a relatively flat trajectory? or is there a magic number somewhere before things start to drop off?
     
  2. c3shooter

    c3shooter Administrator Staff Member

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    Well, this is basically a carbine round- Flat and 7.62 x 39 are not usually used in the same sentence. :p Ballistically, very similar to 30-30.

    If you zero for 4 inches ABOVE the aim point at 100 meters, you will be on target at 200- but at 300, about 15 inches low. Energy also starts dropping faster than a politician's promises.

    Myself, would zero about 3" high at 100 meters, and keep my shots to 200 meters, and you can "Hold on hair, never air".
     

  3. robocop10mm

    robocop10mm Lifetime Supporting Member Lifetime Supporter

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    Be careful of nomentclature in ammo. I have never heard of 7.62X39R. The R means "Rimmed". There is a 7.62X54R that is tbe Russian Mosin Nagant ammo. There is 7.62X39 (no R) that is the SKS/AK ammo.

    A 100 yard/meter zero is perfectly fine for either ammo. The X39 is not well known for accuracy or energy much beyond that. In a bolt action rifle (do you have a CZ?) I would consider it a 150 yard max cartridge for medium game like smaller deer.
     
  4. SoL

    SoL New Member

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    my apologies, i was under the incorrect impression that the r standed for Russian. Rimmed makes much more sense, i'm talking 7.62x39 as in AK47 and SKS. I think i'll go for bang on at 100 actually, whats the bullet rise likely to be short of that, say I zero it for 100 and shoot a rabbit at say 50 or 60 metres, am I going to have to aim notably low to compensate?
     
  5. c3shooter

    c3shooter Administrator Staff Member

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    Nothing shoots flat, except a light beam. Bullet will cross the line of sight going UP, and then back DOWN again to meet the target at the zero point. Just WHERE it crosses will depend on several variables, most notably how high your sights are above the line of the bore, and how fast that bullet travels. A scoped rifle has a line of sight quite a bit higher than iron sights. Get it zeroed at 100, then without changing any sight or scope settings, fire at 50 yards, 25 yards, and see where YOUR rifle is printing.

    Now, just for sake of argument, if your sights are 1/2 inch above the bore, and you are shooting a 123 gr bullet at about 2010 fps, with a bullet having a B/C of .256, and it is zeroed at 100 yards, 70 degree day, 50% relative humidity, and had Cheerios for breakfast, the bullet comes UP thru the line of sight at at 15 yards, at 50 yards is about 1 inch ABOVE the line of sight (aim lower) and drops back to point of aim at 100 yards. Now, I could teach you how to calculate that for a small fee- or just do what I do- and cheat- use a computer.
    http://www.handloads.com/calc/
     
    Last edited: Mar 29, 2010
  6. SoL

    SoL New Member

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    We don't have Cheerios, 70 degree days or relative humidity.
    My mum once bought me some from a specialty shop once when i was a kid and all i can remember is I thought they were ****e.

    I am actually quite an experienced shooter so know all the theory and such, but for the past 7 years I've only worked with shotguns and rimfires which, of course, utilise that same theory, but on a much smaller scale. Now extending into centre-fun i've got to be thinking beyond 100-150 metres, which up until now was largely unheard of shooting rabbits and possums in thick thigh high brush and shotgunning or LR-ting them at ranges generally less than 30m.

    New territory for me! So I just thought I'd ask if anyone had the basic statistics of the steelcore milsurp rounds i have, norinco produced i think.
    ie muzzle velocity (fps of mps) and figures relating to the rifle being zeroed at 100m. Will be XXX" high at 50m and XXX" low past 120m.

    Now reading it i realise it's a mean question, but an answer would be VERY useful :)
     
  7. deth502

    deth502 New Member

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    im judging by your posts that you are not in the us.

    if you were, the norinco steel core has a mild "collector value" here, due mainy to the fact that ammo can no longer be imported here from china. you could probably sell the norinco and turn that money back into more ammo, or, the same amount of ammo and a bit of spending money.
     
  8. c3shooter

    c3shooter Administrator Staff Member

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    Sol- apologies- sometimes I pull someone's leg, and have if come off at the knee. Was just kidding about the Cheerios- but the rest of the answer I gave you should be pretty close to accurate for a milsurp 7.62 x 39 round. That will be roughly the muzzle velocity, that is roughly the ballistic co-efficent of that round, etc. And the numbers I gave you should be pretty close to accurate. Temperature DOES affect the flight of a bullet- colder air is denser, and will slow a bullet more than warm air, meaning it drops more- but that really becomes noticeable at 500 meters and more. For 100 meters, unless you are shooting in the arctic in winter, or Saudi Arabia in the middle of summer, may not matter enough to notice. Same for humidity- more humid air is denser than dry air.

    The link I gave you is to a real ballistic calculator- plug in the variables, and have it crunch the numbers.

    So where in the world ARE you?
     
  9. SoL

    SoL New Member

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    hwee! That's perfect, just got back from a trip inland today during which i had a play with the 7.62. slightly overkill shooting rabbits but it was definitely fun and also quite heartening how accurate centrefire stays at the ranges I have only ever dealt with, it was brilliant. Tried to use the 243 also but it's scope was wanky.

    I'm in New Zealand :) We have an explosive rabbit problem in the central south island.
    they just keep exploding and its unsafe! No, there is just a massive amount of them and subsequently the land is absolutely desolate and raped, so we protect vineyards by shooting them en mass.

    We use subsonic .22LR so i'm very accustomed to significant holdover and arcy bullet trajectories, it's very friendly to find how easy centrefire is :) I was worried.
     
  10. ccd8541

    ccd8541 New Member

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    This is not correct, it is the opposite.
     
  11. Mack Bolan

    Mack Bolan New Member

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    you sure about that....?

    humidty is moisture in the air, and therefore of a denser quality then dry air...

    this is why helicopters dont do well in humidity...denser air>>> less flow>>>>less lift...

    pretty sure c3shooter is correct
     
  12. ccd8541

    ccd8541 New Member

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    Sierra - exterior ballistics
     
  13. IGETEVEN

    IGETEVEN New Member

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    WHY IS MOIST AIR LESS DENSE THAN DRY AIR
    T SAME TEMPERATURE
    METEOROLOGIST JEFF HABY

    The units of density are mass divided by volume (m/V). Density will increase if either mass increases while the volume remains constant or if volume decreases while mass remains constant.

    Density of air will vary as the temperature and moisture content in the air varies. When the temperature increases, the higher molecular motion results in an expansion of volume and thus a decrease in density.

    The amount of water vapor in the air also effects the density. Water vapor is a relatively light gas when compared to diatomic Oxygen and diatomic Nitrogen. Thus, when water vapor increases, the amount of Oxygen and Nitrogen decrease per unit volume and thus density decreases because mass is decreasing.

    The two most abundant elements in the troposphere are Oxygen and Nitrogen. Oxygen has an 16 atomic unit mass while Nitrogen has a 14 atomic units mass. Since both these elements are diatomic in the troposphere (O2 and N2), the atomic mass of diatomic Oxygen is 32 and the diatomic mass of Nitrogen is 28.

    Water vapor (H2O) is composed of one Oxygen atom and two Hydrogen atoms. Hydrogen is the lightest element at 1 atomic unit while Oxygen is 16 atomic units. Thus the water vapor atom has an atomic mass of 1 + 1 + 16 = 18 atomic units. At 18 atomic units, water vapor is lighter than diatomic Oxygen (32 units) and diatomic Nitrogen (28 units). Thus at a constant temperature, the more water vapor that displaces the other gases, the less dense that air will become.

    You may be familiar with the concept that moist air is less dense than dry air. This is true when both have the same temperature or when the moist air is warmer. Said in another way, air with a greater percentage of water vapor will be less dense than air with a lesser percentage of water vapor at the same temperature. Often people erroneously believe that moist air is denser than dry air because very moist air is more difficult to breathe than dry air.


    It can be confusing, we all have learned something new today gentlemen! :)

    Jack
     
  14. c3shooter

    c3shooter Administrator Staff Member

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    CCD is correct. Will plead diminished capacity. Or TWI- Typing while imbibing. But I am still wanting to try one 2000 meter shot fired ACROSS the North Pole- just to see what happens! :p