High power rifle trajectory

Discussion in 'The Powder Keg' started by Dale, Oct 20, 2002.

  1. Is it a correct belief that, as a general rule with all things considered, that the trajectory of a high powered rifle round rises after firing?

    If so, is it also correct in assuming that if the trajectory is 2" below POA at 25 yards it will be 1" above dead center at 100 yards?
     
  2. Klaus

    Klaus Guest

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    All bullets fired from a gun form a kind of squashed parabola because they are under acceleration from gravity and air resistance. Small arm bullets do not generate lift.To make up for the distance the bullet falls in flight, the barrel must be angled up slightly. This means the bullet will impact a little high if you sight in at 200 yards and then shoot a target at 100 yards without compensating. There is nothing magical about it. If the barrel is NOT elevated, the bullet will always hit below the aim point. Note: I am talking about sight adjustment here. The bullet ALWAYS drops below the bore line, no matter how the gun is angled, short of straight up or down.
     

  3. Mandy

    Mandy FREE CITIZEN Forum Contributor

    :assult: :assult: :assult: :assult: :assult:

    Right on Klaus!, that's phisics plain & simple
    the mathematic explanation of this can be found in any phisics text book in the section refering to projectiles.
    For those of you that like to do your numbers.

    :assult: :assult: :assult: :assult: :assult:
     
  4. guffster

    guffster Guest

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    Klaus is right as usual. The law of gravity is at work the momemt the bullet exits the barrel, pulling it steadily towards the ground.
     
  5. The answer is

    Howdy Klaus!

    Spot on as usual.

    Hypothetically, if you are spot on at 50 yds, you'd be high at 25 and low at 75 and lower still at 100. That is if you fix the crosshairs at the same aim point on a target.

    :target:
     
  6. Then, I must be missing the boat here.

    Mausers are known to be accurate (zeroed) at the factory for 200-300 meters).

    That means to do so the bullet has to go up for a certain amount of time before the gravity brings it back down to zero....right? Or am I wrong here.

    That's my problem I have trouble understanding.

    I have three that shoot lower at 25...higher at 50 yards...even higher at 75 yards and higher yet at 100 yards.

    I'm just trying to understand this thing here.
     
  7. wes

    wes Guest

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    The bullet is going in an arc, zeroed at 200 M. At 25M the bullet is still rising,same thing under 200M,still reaching the top of the arc,at 200M it's at the top of the arc and desending below the SIGHT line,not the BARREL line.
     
  8. dave375hh

    dave375hh Guest

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    Dale,
    Your confusing line of sight(the sights no matter what kind) and line of departure(the angle the bbl is elevated relative to the line of sight)The bullets flight in a normal set up will pass through the line of sight at about 25-30yds then fall back through the line of sight somewhere down range where this happens is referred to as your zero range. If the barrel and the line of sight are on a dead level, the bullet won't ever cross the line of sight. This is because the bullet starts dropping from gravity as soon as it leaves the barrel.
     
  9. Thanks, Dave, there's my answer.

    I never made my issue quite clear, I see. But here it is:

    I've mentioned many times, with my eyes, I can't shoot 100 yards well enough to zero any of my guns with open sights.

    I can barely manage 75 yards......but, I can manage.

    Fifty yards seems to be my max as far as sight zeroing goes.

    So, I have many guns that I know, by design, shoots high at 100 yards.

    IF I aim dead center at 25 yards and it hits 6" low but at 50 yards it hits 4" low. At 75 yards it hits 2" low. Knowing that that particular bullet is climbing at that rate can I assume it will be dead center hits at 100 yards? Or is that impossible to guess?

    I was just wondering the feasability of zeroing in a weapon for 100 yards WITHOUT shooting the 100 yard distance.
     
    Last edited: Oct 21, 2002
  10. oneastrix

    oneastrix G&G Newbie

    Very interesting post....Good info given by all.....I know I learned something from this thread......

    Dale, we always zero'd our dept AR15's at 25 yards....Never had a problem hitting at 50 or 100 with them as a result. Does that sound correct?
     
  11. dave375hh

    dave375hh Guest

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    Dale,
    If you sight in so the impact at 25yds is at point of aim with iron sights you will have about a 75yd zero with most C/F cartriges. Using a scope the 25yd zero wiil result in a zero of about 100-110yds because the scope line of sight(LOS) is higher relitive to the bore and the bore would be elevated more to cross the LOS at 25yds. remember the LOS is a flat line and the bullet path is a constantly increasing arch(as the bullet slows it drops faster).
     
  12. Shaun

    Shaun G&G Evangelist

    Klaus is definitely dead on regarding this for instance to get a 375H&H out it its futherest range the barrel would have to be set at a 31 degree upward angle. using a 270gr bullet at 2900 fps it will hit the ground some 5500 yards later

    in a 308 wcf using the federal match load for instance or the M2 ball Match ammo and hit a human size target at 1000 yards the point of aim would have to be approximately 18' over the point of impact.
     
  13. Klaus

    Klaus Guest

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    Dale, I have thought about the trajectory you described, and it makes little sense unless your sights are mounted VERY high above the barrel. What did you mean about aiming "dead center" at 25 yards? Did you use some kind of boresight?
     
  14. I appreciate everyone's brainstorming on this issue but perhaps we need to drop it, as I am getting confused even more so, lol.

    Here's the story in a nutshell: Saturday when I was at the range I took the Mosin 91-30 along and it was shooting about 6-8 inches high at 50 and 75 yards, respectively.

    I know my original Swede also shot high and I replaced the front blade to correct it but with the Mooin I wasn't sure if I could find a higher front sight pin for it. But, hoping I could I got to talking to this guy who was shooting on my right about my inability to clearly see the 100 yard target for sighting.

    He said if you know your bullet weight, powder, etc. you can calculate where to sight in at shorter range in order to have 'right on' hits at, say 100 yards.

    He drew some diagrams....did some calculations I couldn't keep up with to explain his thoughts.

    I just thought I would bounce it off you guys to see if I could 'get back on track' with what this guy was saying.

    He gave an example on one of his guns saying, knowing the specifics of the bullet, charge, cartridge, etc. his was hitting slightly high at 150 yards. Based on his own calculations he determined that, with the arc of the bullet, if he sighted in at approximately 15 yards it would be on at 150 yards.

    It was just confusing to me and he could well have been full of BS and trying to impress me.

    I realize the issue of the arc of travel even with the barrel level and I also know that consistant 'right on hits' would vary depending on the ammo....the bullet weight, amount of charge, velocity, etc. unless that, too, is consistant.

    When I get a front sight pin I will worry about it then....but, again guys...thanks anyway and sorry I confused you all, as well as myself :)
     
  15. Mandy

    Mandy FREE CITIZEN Forum Contributor

    Dale:
    I think the explanation about the arc that the guy told you just may be true.

    The arc described by the trajectory of a bullet is similar to the shape of an extended parable facing down.

    If you measure the height of the trajectory along the horizontal axis, you'll find that for each value of nearer X1 you'll have the same height for a value of farther X2.

    This is complex math and to do this you must have a lot of formulas and data so you can derive the actual formula for the expected parameters (bullet weight, powder charge, bullet shape, relative humidity, air friction, gravity, ect.).

    Probably, someone has allready done it and maybe this formula can be obtained somewhere.

    In the example below, the X1 value of 50m have a height of 20ft, the same as the value X2 of 250m.
     

    Attached Files:

  16. Shaun

    Shaun G&G Evangelist

    The quickest way to see what is being talked about is to pick up a copy of the Sierra Ballistics software it will show the bullet drop and all you have to key in is muzzle velocity and zero yardage