Ballistics chart not correct for me...what am I missing

[tonysnoo]

I shoot a couple of different calibers in steel matches. Both are 6mm. The 108 Berger works the best for me.

I use a magnetospeed and have worked the dope backwards too. I like to use the uncorrected pressure with 0 for altitude for our calculations. We shoot at altitudes of 4200 to 6200. We seem to range from 24.6 to 25.8 in station pressure. We have used multiple range finders to verify the distances we shoot at. There is some slope involved that is not factored in but pretty slight.

Both calibers (6SLR@3090 and 6Fat Rat@2860) seem to follow the dope up to 550 pretty spot on, but at 850 the actual is about a minute less than the dope says to be at. My buddy has the same problem with his dope and 108s.

We have worked the dope back and forward. If we change temps, BC, pressure, etc to get the 850 correct the dope is off for our closer ranges.

Each rifle has different brands of scopes I have seen this problem with hybrids too but not as bad. I wonder if altitude changes the bullet path and somehow allows it to stay afloat longer???? Am I doing the calcs incorrectly???

The reason I am concerned is that we are starting to play with tacticool matches and I want to have a good feeling that my calculated dope with work at any of the longer distances....right now it doesn't.

Ideas anyone?

 

[Jammer Six]

Go with what is, ignore what should be.

 

[tonysnoo]

Go with what is, ignore what should be.

seems reasonable and I do that at our known distances in our local matches...but unless I shoot at a bunch different distances, and document them, I could go to an out of town match with different firing solutions needed and always waste the first shot(hopefully only one) of a stage figuring out come-ups.

I have also used an app called shooter to input multiple actual range vs come-ups values. It just give me speed(coincidentally the same as measured). When I apply that speed to its calculator, I still get the same dope that AP gave me....go figure???

 

[ZenArchery]

I have used 4 different Ballistic Apps. They all have their falling off stage depending on input variables and the algorhythem they compute out. My experience Apps are good between 400-800 yard's max for all Apps I use. Then it comes down to external ballistics, environment and "shooter." Apps are good to get you close but your ability to put in right data and the apps abilities varies.

 

[boltfluter]

I would check the click value on your scope to make sure it is in fact .25 moa or .1 mil depending on which one you are using. Some bal programs will allow for a correction factor. Just a thought.

Regards, Paul

www.boltfluting.com

 

[JohnKielly]

Have you considered that your chosen ballistic program is the fault?

 

[boltfluter]

Also check to make sure your scope height above the bore is spot on.

Paul

www.boltfluting.com

 

[CharlieNC]

Beyond 550 is where the effects of "minor" input errors begin to show up significantly, and accumulate. For example your dope at different altitudes will not be very different within that range. Double check that your ambient conditions are correct. Are you accounting for verticle angle and temperature effect on velocity? Wind from the right can make you shoot high, up to 20% of the windage drift. Fine tuning these give me good verticle calcs.

 

[bobinpa]

I don't think I have ever had a chart that was dead on all the way to 1000 yds. The smallest change or incorrect input can make a big difference out past 500 - 600 yds. Your input isn't necessarily wrong but it may be unknown. You may generalize that the humidity will be 65% and it may end up being 80%. If you input the wrong scope height by .25" or the humidity is off it can have a considerable affect. To me, the only surefire way is to verify my charts in real application.

 

[Catfish]

I have played with a lot of drop charts and found that what the computer says and what happens in the real world never seems to be the same. bobbin pa hit the nail on the head. Another thing is that the BC of the bullets listed by the manufacture are not always right on. There are so many thing that effect the drop of the bullet past 500 yards. that I will never use a drop chart that I have not field checked.

 

[nmjwolf]

Also check to make sure your scope height above the bore is spot on.

Paul

www.boltfluting.com

This^

 

[tonysnoo]

Have you considered that your chosen ballistic program is the fault?

Ive used four different programs including AB and they all agree

 

[tonysnoo]

Also check to make sure your scope height above the bore is spot on.

Paul

www.boltfluting.com

Yup, spot on....Ive even adjusted it in the programs just to see what effect...still coulnt get em to jive at all my known distances.

 

[tonysnoo]

Beyond 550 is where the effects of "minor" input errors begin to show up significantly, and accumulate. For example your dope at different altitudes will not be very different within that range. Double check that your ambient conditions are correct. Are you accounting for verticle angle and temperature effect on velocity? Wind from the right can make you shoot high, up to 20% of the windage drift. Fine tuning these give me good verticle calcs.

I use a kestral and another mountaineering instrument. We all compare notes at our matches...so Im pretty confident in the conditions that are input

 

[tonysnoo]

I would check the click value on your scope to make sure it is in fact .25 moa or .1 mil depending on which one you are using. Some bal programs will allow for a correction factor. Just a thought.

Regards, Paul

www.boltfluting.com

You got me thinking....I have tweeked so many parameters in the various programs trying to get my dope lined up, but never this. I tried a correction factor of 1.047 and the dope skewed the wrong way. I then tried .95 and low and behold my 330, 425, 550, 660, and 850 numbers lined up with my actual dope at those known ranges. Coincidence??? Not sure....Its a great start. I tried it with AB and shooter....both the same results. We are going to set steel at some other distances and see if the program will work.

 

[boltfluter]

I would check the click value on your scope to make sure it is in fact .25 moa or .1 mil depending on which one you are using. Some bal programs will allow for a correction factor. Just a thought.

Regards, Paul

www.boltfluting.com

I would check this. The further out you go the more even a small error is magnified.

Paul

 

[hogpatrol]

Also check to make sure your scope height above the bore is spot on.

Paul

www.boltfluting.com

This ^ and scope reticle in proper alignment and not skewed left or right.

 

[tonysnoo]

agreed....have done it on other scopes on guns that dont align with dope, but not the most recent one. Crosshairs aligned and level...religious about that.

Really still wonder about high elevation and if bullet drop really follows the same curve as low elevation???

 

[ballison]

I doubt it's scope over bore. At longer ranges, that variable and any errors become insignificant. The 2 variables already mentioned that show their ugly heads at longer ranges are atmospheric and scope click values. Could be cant, but that would also show up as windage on your targets. If you haven't run a calibration test on your scope, that would be a good things to start with.

 

[fredo]

Agree with above. I'd put that scope thru its paces with a tall target test & see what ya got.
Sometimes, a scope will track "true" for a bit & begin to crap the bed with increased erector travel. And that error could be repeatable, and the scope still return to zero, so its difficult to ascertain without mapping it out on a big azz piece o' paper...