Re: G7 Ballistics
This is a trial and error method, and some else may have a better one, but this is what I did.
Start @ the JBM Trajectory page.
Select the bullet you want from the bullet list at the top of the page. It must have “(Litz)” at the end, if you want a G7 BC.
Input all the information you would normally do on this page.
Have the program calculate the trajectory, and either open another page, or copy and save the traj. data to something like MS Word.
Here is where the trial and error starts.
Go back (if you copy and pasted the data, or use the other page you opened and go to the JBM page) to the trajectory input page, and select “none” in the bullet list.
Then use the manual input boxes to input your bullet data.
Make a guess at what the G7 BC is, and plug it into the “BC” box (155gr .308 bullets start around 0.210, and 200+gr .308’s are around the .320’s).
In the little pull down box next to the BC input, select “G7.”
Make sure all other data on the input page is the same as the first one you did (make sure you set the “Maximum Range” to at least 1000 yards on both).
Now compare the drop, at the farthest range, of both trajectory outputs. If they do not match then the G7 BC you guessed needs to be changed. Go back to the previous page, and increase the BC number if you have more drop (with the BC you guessed) than the original, and vise versa.
Keeping doing this until the numbers match perfectly. This will give you the G7 BC that JBM is using to calculate the trajectories for the “Litz” bullets in the library.
If you have any questions, or I missed a step, please post back.