JBM Ballistics online calculator error??

[mikeinfwa]

I cannot determine why the Trajectory Card outputs data that is at odds with my knowledge of ballistics.

Using the "Trajectory Card" I input data for .338 300 SMK Litz
2865 fps
2.4 in scope height
1000 yard zero range
zero temp 80degrees
zero altitude 800 ft

input ranges 1000,1100,1200... 2000
input temps of 20 and 100

output shows LESS bullet drop for 20 degrees vs 100 degrees

20 degrees shows 16.7 mil drop
100 degrees shows 17.6 mil drop

 

[Hondo64d]

Same thing I noticed. Interested in the answer myself...

John

 

[mikeinfwa]

additionally,

When I use Trajectory "drift" or simplified the drops are off significantly past 1700 yards when using the same input data as i did with the Trajectory Card.

2000 yards the difference is 1.0 mils

17.3 mils with the "Card" calculator
16.3 mils with the "Drift" calculator

 

[delfuego]

You guys really shooting on a day from 20-100 degrees with a 1000 yard zero? Just add one temp and one altitude. Better yet just use the Trajectory calculator with standard atmosphere for your elevation and you will be close.

 

[mikeinfwa]

You guys really shooting on a day from 20-100 degrees with a 1000 yard zero? Just add one temp and one altitude. Better yet just use the Trajectory calculator with standard atmosphere for your elevation and you will be close.

No I don't shoot often at 20 and 100.

I inputed those temps to see what the calculator would output...... AFTER I got a 1.0 mil difference when using 2 different online calculators entering the same data.

See my post above.

The "Drift" vs the "Simplified" calculators produce a 1 mil difference at 2000 yards...

Why the 1 Mil difference???????

 

[Matches Malone]

Your data put in is all weird...why is your zero at 1000y? and less drop is normal for colder temperatures...air density.. and its .1 mil higher for wind in hot temp from spin more than likely.

 

[Tempest 455]

I just shot 2,000 yards last weekend and the on-line JBM numbers were right on in the 1st shot for elevation.