B.C. Variance

[Hunter]

Could someone tell me what the best way is of allowing for the change in ballistic coefficients at the various velocities over long range for use in computer trajectory calculations?

For example, a given bullet has BC is .450 at 3100fps, .440 at 2400fps, and .372 at 1600fps. What BC value would one use for an accurate trajectory calculation for the entire range of velocities?

Do any of the software programs that are available allow for changing BC values or do they all make the calculations with just one value?

TIA

 

[RBrowning]

The Sierra Infinity program allows you to enter up to 5 different BC values and the velosity threshold for custom bullets that you set-up in the program. It will also allow you to put in a max range of 8000 yds. That seems a bit long even for the folks around here

 

[Hunter]

RBrowning, thanks. I just got an email from Robert Treece at Sierra and he confirmed what you said. I have a copy of Infinity ordered.

 

[Brent]

RB,
Do you mean five different drag curves like the Oehler Ballistic Explorer program does, which has 7, one of which is for rimfire, or is this something else completely?

 

[RBrowning]

I'm not familiar with the Oheler program so you will have to draw your own comparisons. The Serria Infinity program allows you to define a bullet if there isn't one already in their library. You can put on diameter, weight etc., then you can put in up to 5 BC values and the threshold values for velocity where the BC will change. Generally the lower the velocity the lower the BC. My guess by looking at the values that they post for their own bullets is that you would get a curve if they were plotted. I don't shoot exotic bullets (LRB etc) so I just use what is in the library.

If you do get the software make sure you go to their site and down load the update. It takes a while to download 2.3M but it is worth it - more in the library, more features and runs faster.