Advanced Marksmanship Ballistic FTE Input Help?

[Mo_Zam_Beek]

I am trying to get better at shooting long. I have read enough and I am convinced that some tech will help me.

Previously recorded data includes temp swings between 95 degrees and 30 inches of mercury; to 35 degrees and 28 inches of mercury.

Looking at a .300WM with a 210 VLD @ 2,800 fps - I have used JMB to get some data that is close. I had to futz with the settings to get it close and it is still off - high at closer distances and low at greater distances. Example it is + 0.2 at 825 and low at 1400 by 0.7.

To get Ballistic FTE to read correctly at 1400 (seemed to make sense to set it correctly for my greatest hard data point and let it be close to my others???) I entered the following:

Native drag - G7
BC - 0.33
Vel - 2,800
Use Drag - G7
Zero Atmosphere - use my real time weather inputs for zero
Current Atmosphere - input current conditions
Sight Height - 2" (confirmed via measurement)
Y Intercept - 0
Spin and stability - off
Coriolis Acceleration - off

Now with a 77 grn SMK or a 175 SMK it is basically the same except I am choosing G1 drag for both. Regardless it seems like I am having to screw with the BC and enter a BC that doesn't correspond with either published data or manufacturer's rec's.



How can I improve on this? What should I be reading or doing to learn?

Thank you.

 

[desertHK]

Re: Ballistic FTE Input Help?

Most ballistic program will get you very close to where you want to be, assuming that your measured velocity is correct. What is more important is the field data. This of course is obtained by sending lead down range. It is not too unusual that you have to play around with the BC as well as the velocity to get the doping to confirm with your field data. Don't forget that the MET and ENV data of the location (s) where you gather your field data can influence the field data. An example is where you sight in you gun and chrono your velocity and where you obtain your long range data has a DA that is +5000 compared to your sight in location.

Also, depending on where you live, at 1400 yards, with a velocity of 2800 fps, you may be entering the transitional zone of your bullet. Therefore, the difference may be more magnified.

 

[LoneWolfUSMC]

Re: Ballistic FTE Input Help?

Pay attention to Barometric Pressure v. Station Pressure.