What to do when a dope chart doesn't add up??

[xswanted]

Question for all.

What do you guys do if a drop chart for a given rifle doesn't line up.

i.e. I put in all the goodies and verify the adjustments at my given zero of 200 yards. Then typically 400 yards. Then at 600 yards , but oops, that one doesn't hit the target. Then I'm back on at 800 yards.

This doesn't happen often but what do you do if a given rifle system doesn't want to follow the physics of your dope chart?

Thanks.

 

[Barrel Nut]

...... snip......... I put in all the goodies and verify the adjustments at my given zero of 200 yards. Then typically 400 yards. Then at 600 yards , but oops, that one doesn't hit the target. Then I'm back on at 800 yards.

This doesn't happen often but what do you do if a given rifle system doesn't want to follow the physics of your dope chart?

Thanks.

I've never seen this, but if I did I would immediately conclude that I made some sort of screw up. There is a VERY slim chance that the physics associated with ballistics suddenly changed. They call this stuff Newton's LAWS of motion, not Newton's GUESSES THAT WORK SOMETIMES.

As Master Po might say, "Look within yourself Grasshopper".

 

[eric32]

Have you checked your scope for tracking issues?

What dope system are you using?

Not knowing what caliber you are shooiting. Be sure to true your velocity within 600 yards. Then true your BC after that.

Also terrain will cuase up and down elevation changes.

 

[Terry]

In my experience helping others, actual experience with the gun does not always match the ballistics program. We use a range notebook to record our experience at each distance. We shoot the readings out and back to confirm our notes and the scope.
At that point we confidence with our numbers.

 

[CharlieNC]

I have occasionally experienced that one oddball distance too, and pondered why. My best explanation is I was doing something different, like poor parralax adjustment or recoil control. Shooting prone in the field can easily lead to unusual results due to positioning challenges.

 

[xswanted]

Thanks guys.

I've had it happen over the years on a couple guns.

Right now I use StrelokPro and iSnipe. I also have a G7 rangefinder so between the three I should be able to hit anything any given distance at any given time right?!

The gun in question is a 22BR. It shoots very well and I'm a proficient shooter.

I have the gun zeroed at 200 yards, verified on target at 200 yards. Shooting 75 bergers at 3250 avg. It dials up to 300, 400, 500 and 715 perfectly. In fact last summer over one week I shot one shot a day and had a seven shot group that was about the size of a dollar bill at 715.

All three programs are within a tenth of a minute at all ranges but at 600 yards I miss my gong regularly. The other distances are dead nuts. It seems like it is USUALLY high.

Is this/could it be parallax? I've even shot this load to 850 yards and been on target.

I've been frustrated with that distance for awhile now and can't quite figure it out. I have not shot on paper at 600 to see where I'm hitting so, realistically I'm proabbaly not doing anyone any good by asking this without knowing where the shot is going.

 

[xswanted]

Have you checked your scope for tracking issues?

What dope system are you using?

Not knowing what caliber you are shooiting. Be sure to true your velocity within 600 yards. Then true your BC after that.

Also terrain will cuase up and down elevation changes.

This is all shot in eastern ND so elevation is very consistent. Using iSnipe, StrelokPro and a G7 rangefinder.

I have used a 6.5-20 vx 3 in the Gun and it has tracked reliably thus far. Recently I switched to a vx-6 that has also returned to zero but have not shot 600 yards with it yet.

 

[CharlieNC]

Your scope may have a tracking problem at that moa setting. Try shooting with the 600 dope at 100yd to see if it comes up the correct moa.

 

[SheepDog]

First and foremost a dope sheet is what you get from actually firing the gun at the distance. A ballistics spreadsheet will get you close but it is unlikely that it will be as accurate as measuring the group you just fired. I have written two ballistics programs and I'm working on another and I am the first to tell you that "all the variables" can not be measured or input into the program. It is an approximation of the flight of the projectile within the tolerance of localized air density and currents.
Why? Because the ballistic coefficient of the bullet changes over its velocity, the air density can change over the course of flight and the current of the air can be up, down, from the right or left or head wind or tail wind and it can change many times over the bullets flight.

Just because the bullet path is generated on a computer doesn't mean it is correct for any given shot.

 

[eric32]

Thanks guys.

I've had it happen over the years on a couple guns.

Right now I use StrelokPro and iSnipe. I also have a G7 rangefinder so between the three I should be able to hit anything any given distance at any given time right?!

The gun in question is a 22BR. It shoots very well and I'm a proficient shooter.

I have the gun zeroed at 200 yards, verified on target at 200 yards. Shooting 75 bergers at 3250 avg. It dials up to 300, 400, 500 and 715 perfectly. In fact last summer over one week I shot one shot a day and had a seven shot group that was about the size of a dollar bill at 715.

All three programs are within a tenth of a minute at all ranges but at 600 yards I miss my gong regularly. The other distances are dead nuts. It seems like it is USUALLY high.

Is this/could it be parallax? I've even shot this load to 850 yards and been on target.

I've been frustrated with that distance for awhile now and can't quite figure it out. I have not shot on paper at 600 to see where I'm hitting so, realistically I'm proabbaly not doing anyone any good by asking this without knowing where the shot is going.

Seems you have gathered a sufficient amount of dope data for other yard lines. This leads me to believe they might be a scope tracking issue at that particular adjustment range. A tall Target test would either confirm it is a scope issue or not.

I have used Strelok PRO with extreme success on first round hits in various target sizes during PRS matches.

If it was me i would check the scope to make sure it was tracking correctly up to the 600 yard adjustment range. you might have some slack in that part of the scope. Its easy to adjust for you just have to know its there.

First and foremost a dope sheet is what you get from actually firing the gun at the distance. A ballistics spreadsheet will get you close but it is unlikely that it will be as accurate as measuring the group you just fired. I have written two ballistics programs and I'm working on another and I am the first to tell you that "all the variables" can not be measured or input into the program. It is an approximation of the flight of the projectile within the tolerance of localized air density and currents.
Why? Because the ballistic coefficient of the bullet changes over its velocity, the air density can change over the course of flight and the current of the air can be up, down, from the right or left or head wind or tail wind and it can change many times over the bullets flight.

Just because the bullet path is generated on a computer doesn't mean it is correct for any given shot.

I am curious to ask what are the names of the programs you have written? Strelok adjust BC for a speed and environment based on both velocity and twist rate.

the changes in weather you are talking about cant really be shot. what i mean by that i, i am not that good to shoot the difference of .2 mils at 800 yards. when the targets are 15 inch gongs or bigger.

 

[ronemus]

You need to carefully review the inputs to your ballistics program. You certainly want to us a G7 BC, or even better a custom drag curve. Most commercial bullet makers don't publish G7 BCs, but it is possible to convert G1 to G7; the curves are parallel at moderate velocities (~2000-2700 fps IIRC) so there is a fixed ratio (G7 = G1 x 0.38 IIRC). Most G1 data is measured at moderate velocities, so the conversion usually works well. Banded G1 BCs such as Sierra provides are a coarse approximation to a correct drag curve; if the curve is correct, BC is constant vs. velocity.

Other factors include the height of the scope above the bore (measured, not the program's default 1.5") and weather (temperature, barometric pressure, and RH) and wind speed (wind drift doesn't produce a horizontal line - it's actually slanted).

 

[xswanted]

First and foremost a dope sheet is what you get from actually firing the gun at the distance. A ballistics spreadsheet will get you close but it is unlikely that it will be as accurate as measuring the group you just fired. I have written two ballistics programs and I'm working on another and I am the first to tell you that "all the variables" can not be measured or input into the program. It is an approximation of the flight of the projectile within the tolerance of localized air density and currents.
Why? Because the ballistic coefficient of the bullet changes over its velocity, the air density can change over the course of flight and the current of the air can be up, down, from the right or left or head wind or tail wind and it can change many times over the bullets flight.

Just because the bullet path is generated on a computer doesn't mean it is correct for any given shot.

Sorry I don't know all the terms.

The original question is, why would it work at a multitude of distances and not at a certain distance?

Given the scenario you wrote about here, it's likely that even a dope chart won't give you an accurate fisrt shot hit unless you've prepared accordingly in a nearly an infinite number of variables.

I've shot this particular gun in a lot of atmospheric conditions and it seems it's "trouble area" if you will, is ~600 yards. So my confusion with the ballistics is why the three programs I am using would all be wrong at that given area. It seems, as others have said it could possibly be the scope not tracking correctly through that certain range.

Thank you for the reply though, all info is good!

 

[xswanted]

You need to carefully review the inputs to your ballistics program. You certainly want to us a G7 BC, or even better a custom drag curve. Most commercial bullet makers don't publish G7 BCs, but it is possible to convert G1 to G7; the curves are parallel at moderate velocities (~2000-2700 fps IIRC) so there is a fixed ratio (G7 = G1 x 0.38 IIRC). Most G1 data is measured at moderate velocities, so the conversion usually works well. Banded G1 BCs such as Sierra provides are a coarse approximation to a correct drag curve; if the curve is correct, BC is constant vs. velocity.

Other factors include the height of the scope above the bore (measured, not the program's default 1.5") and weather (temperature, barometric pressure, and RH) and wind speed (wind drift doesn't produce a horizontal line - it's actually slanted).

All the inputs are measures as accurately as I can do it.

The problem persists only at the area around 600 yards. Past that the charts line up and closer they line up.

Could be the scope, or I have put in my info in incorrectly and somehow I'm fudging the other distances.

 

[fredo]

If your scope's reticle has (mil or moa) subtensions, see if you can hit that 600yd target using a reticle holdover.

If you can hit with a doped holdover, but not with a dialed correction, it's a pretty good indicator that your scope has pooped the bed. Its a leupy, so that wouldn't be anything surprising...