Help With Ballistics PLEASE!

Discussion in 'Rifles, Bullets, Barrels & Ballistics' started by matt_3479, May 14, 2011.

  1. matt_3479

    matt_3479 Well-Known Member

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    Yesterday i tried to do some quick yet extensive shooting at ranges from 100-450 yards just to begin to test this ballistics program i used and i was spot on at 100 with a 1/2" group so we know the rifle can do it. But then i backed up to 200 and which i was almost 1-1/2" low. So i checked the program and it said i shouldn't have been. I backed up too 300 and i wasn't even on paper any more and i couldn't figure out what the hell was going on!. I backed it out too 450 and 1 bullet it the bottom right out of 3. So i moved it back into 200 same thing happened. I moved it out too 300 and added 1 1/2 moa and i was on paper this time and then too 450 and added a few moa and this time i was decent.

    I would like some help with a ballistics program you guys are using? Im using 243. win, 80 grain factory loads with BC of 0.365 fired at 3330 FPS.

    Im trying to practice out too 600 yards but if i cant get too 300 i dont know what to do.
     
  2. Wingnut

    Wingnut Well-Known Member

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    Did you just use the manufacturers numbers on velocity and BC? The program will only be correct if you use the corrected BC for your ammo out of your gun. What you want to do is zero the rifle at 100 or 200 yards which ever is the best for you. If you can reset your turret to zero at that range. Use your ballistic program to get you close at a longer range. The longer the better you can shoot. You can either shoot at the longer range and shoot for center or just shoot a group and measure the distance of the group to center. Some programs like G7's, gseven - Home, you can just input the measurement from center to save you some shooting. This will give you actuall data out of your rifle. Then the program will give you an adjusted BC for your rifle. Use this data to print a drop chart for your rifle and it will be right.
     

  3. royinidaho

    royinidaho Writers Guild

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    Build youself a target as shown in the first image on this thread Long Range Targets It doesn't need to be that tall but tall enough for you to hit the single target at the top @ 100 yards.

    Read the article and shoot at your several distances. At each distance aim at the target at the top.

    This will reveal your drops.

    Use JBM to figure the BC out to your max distance.

    Then dial the turrets for each distance. Make corrections as necessary.

    I've been told that doing it this way will result in being off by the cosine of gravity. Thus the dialing and adjusting to check things out.

    Hope this helps.

    I did this once out to 1200 yds. Took all day and I was one tired little boy. It helped.
     
  4. LouBoyd

    LouBoyd Well-Known Member

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    Make sure you have the correct value for the height of the centerline of your scope over the centerline of your rifle bore entered in your ballistics program. Don't guess, measure as precisely as you can. All ballistic programs have an entry for that value.

    It will wreck havoc if with all downrange drop calulculations the ballistic program gives if you get it wrong. It causes increasingly greater error as the range increases.

    Getting the atmopheric measuremets entered is importat too, but that's not very important at 300 or 600 yards unless the values in th program are way off, such as shooting at high elevations. Of course you need the correct bullet BC and muzzle velociity in the program. No ballitics program is better than the data you give it.
     
    Last edited: May 15, 2011
  5. trebark

    trebark Well-Known Member

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    Ran your numbers in Exbal at sea level and 100 yard zero. Here's the data....

    Will gladly rerun the chart if you can provide more accurate data such as altitude, temp, pressure, sight height above bore
     

    Attached Files:

  6. bigngreen

    bigngreen Well-Known Member

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    Through out what all your data was so we can help better, ballistic programs have a learning curve so just keep hacking away at it! :D
     
  7. dig

    dig Well-Known Member

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    2nd on the scope hight, would not have thought it made that much difference but at 780 out of a 300 Wby I was off by just over a .25 inch and it made 9 inches of adjustment trouble, any body have a best way to measure?
     
  8. LouBoyd

    LouBoyd Well-Known Member

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    There are several ways to measure. It depends on what parts of the rifle you can access.
    1. One method is to find a place where the diameter of the barrel and the diameter of the scope can be accessed in a single plane perpendicular to the line of sight with the scope zeroed. Measure three things.
    Ds = diameter of the scope in that plane
    Dr = diameter of the rifle action or barrel in that plane
    Sp = space between the scope and the rifle in that plane.
    H = the height of the scope over the bore

    H = Sp + (Ds+Dr)/2
    The above method only works if the barrel or action and scope are round and concentric with the line of sight and bore.

    Other methods.
    2. Find a place where the barrel and scope are approximately the same diameter then measure the distance from a point tangent to the scope and tangent to the barrel, perpindicular to the line of sight. Agian, the barrel and scope must be round and symetrical.
    There are variants on the above methods which accomplish the same thing. These metods are not correct if the line of sight and the bore centerline aren't close to parallel. The rifle and scope must be round and conentric as in #1.

    3. For high accuracy zero the scope on a target at the distance you'll use in your ballistic software. Mount a digital camera with a focusable lens on a claibrated linear slide set a few feet in front of the muzzle with the slide (or the rifle) adjusted to move in a line perpendicular to the line of sight and will move toward the centerline of the barrel. Move the camera so it'centered and focused on the zeroed reticle looking into the scope. Then by moving the camera only in the direction perpendicular to the line of sight, measure the distance the camera must be moved to be centered on the crown to the same same pixel on the CCD camera image as the reticle was zeroed. The direct measurement of how far the camera was moved is the scope height over the bore.

    I have this equpment set up in my shop. It's very fast once the equipment is set up and will measure the rifle's scope height with no guessing to better than .001" I just lay the rifle on its side on a roll around table in front of my mill while using the mill vise to hold the camera and make the readings using the mill's DRO to .0001". Other linear slides will work like the carriage of a lathe or the spindle of a drill preess. This method will give the correct measurement even for very long zero ranges and with wedged scope bases where the bore centerline and line of sight not parallel and the line of sight is not centered on the scope's body.

    I use a laptop with a USB camera. THey're not expensive but it helps to have one with a long enough focal length lens to get a clear image of the reticle and crown and it must be able to focus on the reticle and the crown. The cameras built in to laptops don't work well.
     
    Last edited: May 17, 2011