Ballistic chart just don't match the real world. Need some help.

[4ked Horn]

Ballistic chart just don\'t match the real world. Need some help.

Hey everyone. I'm back and I have a question. I am trying to work up a drop chart for my bro and for the first time I am unable to make the program I use match the real world results close enough for my satisfaction. I need some help crunching the numbers.

Load data:
69.5 gr of h4831sc.
250 gr sgk .338 cal
mv 2575
Published bc:
.565 @ 2500 fps and above
.563 between 2500 and 2000 fps
.550 between 2000 and 1600 fps
.537 @ 1600 fps and below.
Testing conditions:
scope height 1.625
temp about 60 deg
altitude 2800 feet above sea level.
Tested trajectory
100 y 0
200 y not shot
300 y 4.25 moa
400 y 7 moa
500 y 11 moa.

We shot 3 shot groups and adjusted the scope then reshot to confirm. Now I am trying to make a ballistic program fit this curve so I can calculate drops for every 25 yards out to 500 on a level field then recalculate these same drops on a 30 degree slope. Also the elevation we will be hunting will be from 3700 to 5500 feet altitude. I also would like to calculate wind for these charts with a 10 mph full value cross wind.

I would really like some help making a ballistic program match the points we have shot OR I would like someone to email me a spread sheet with the level drops and the sloped drops at 4000 feet elevation with coresponding drift info all in 25 yard increments. The sooner the better would be very very appreciated.

[email protected]

Thanks.

 

[royinidaho]

Re: Ballistic chart just don\'t match the real world. Need some help.

Sent you a spread sheet.

It takes the actual drop only into consideration. The more data points the more accurate the prediction.

Using actual data and doing a curve fit automatically takes all the other stuff (scope height, etc.) into consideration.

Gotta love those 338 Winnies. They shoot a bit of a rainbow but there's a big thump at the pot of gold. /ubbthreads/images/graemlins/cool.gif

 

[4ked Horn]

Re: Ballistic chart just don\'t match the real world. Need some help.

Thanks Roy. that looks great. would it be possible for you to run the same program that gave you the chart you sent but this time with a 30 deg slope factored in? I should be able to do the wind part of the calculation as that is less drastic of a change.

We're going hunting in the morning and all this stuff is piling up as usuall.

 

[royinidaho]

Re: Ballistic chart just don\'t match the real world. Need some help.

Done deal.

Check the calc cell for the calculation of cos of 30 deg in radians.

Was impressed with how much even a small slope of 10 degrees affected POI

its in namail

 

[4ked Horn]

Re: Ballistic chart just don\'t match the real world. Need some help.

got it. thanks. i'll keep you posted on how things go.

 

[Guest]

Re: Ballistic chart just don\'t match the real world. Need some help.

[ QUOTE ]
Using actual data and doing a curve fit automatically takes all the other stuff (scope height, etc.) into consideration.


[/ QUOTE ]

How are your *fitting the curve*? Linear interpolation? Splines?

 

[royinidaho]

Re: Ballistic chart just don\'t match the real world. Need some help.

The way I figure it is that WYSIWYG, don't know how good that thinkin' is /ubbthreads/images/graemlins/blush.gif

Just using MS spread sheet and using trend line option and getting the most R^2 9s or a 1

Usually a 2nd/3rd or 4th order poly will be really close if there are enough accurae data points upon which to base the fit.

The rifle has to shoot really well for it to work.

And its only good for the conditions under which the baseline shooting was done.

I'll send what I sent to 4kd.

 

[4ked Horn]

Re: Ballistic chart just don\'t match the real world. Need some help.

[ QUOTE ]
How are your *fitting the curve*? Linear interpolation? Splines?

[/ QUOTE ]

Mostly doinking with the bc and drag functions and velocities to get what we had happen at the range line up with our 100, 300, 400 and 500 yard calculations.

(sorry it took so long to respond. kinda got real busy, real sudden like.)

 

[4ked Horn]

Re: Ballistic chart just don\'t match the real world. Need some help.

Roy, your help was a big help. we ran into another obstacle we had no idea was coming. At one point Bro was hunting with a buddy and had a 350 yard shot on a 4 point (western count) and missed by 24 inches low??? /ubbthreads/images/graemlins/shocked.gif We fired a test shot the next morning to discover he had shot his range shots with his left hand resting on the scope. this (we think) was enough to cause the bbl to touch the forend and raise the impact at the range. Then when he shot at the deer and didn't have his hand in the same place the bbl sagged to its correct position and the shot went low.

All that worry and fuss and then having to go back to the drawing board. I think a quick morning at the range and a quick scope adjust should fix the problem. Then we should have the time to play with some programs and get more input on how to get the right calculations.

Again thanks for your help when we needed it done real quick.

 

[royinidaho]

Re: Ballistic chart just don\'t match the real world. Need some help.

Bummer /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/crazy.gif

 

[4ked Horn]

Re: Ballistic chart just don\'t match the real world. Need some help.

We figured it out in time for the end of elk season!!!! The scope got cranked down exactly 1 revolution by mistake. 4 shots at the range and all was well /ubbthreads/images/graemlins/blush.gif. We wont make that mistake again.