Calculating Ballistic Trajectory

[treillw]

So I have a few data points from my rifle and I'm trying to get them to match up with a velocity and BC to make a best fit trajectory to enter into my G7 rangefinder. I'm having trouble doing it manually on the G7 calculator. Is there a program that is sophisticated enough to change the velocity and BC at the same time to develop a best fit trajectory for multiple field points? Here are my points.

Point 1: 25.53 hg, 560 yards, actual field correction 8.75 MOA, equivalent velocity calculated using G7 3008

Point 2: 24.75 hg, 405 yards, actual field correction 4.25 MOA, equivalent velocity calculated using G7 3217

Rifle Data: Sight Height = 1.8", velocity 2880, BC .691, 100 yard zero

Clearly the velocities aren't close enough to average, so I'm thinking it's a combination of velocity and BC adjustments that need to be made to develop the trajectory accurately? Any help is appreciated.

Thanks!

 

[WildRose]

Is the velocity you are giving us supposed to be MV or velocity at each of those ranges?

What bullet are you using? Are you chronographing your loads or just trying to rely on the range finder to calculate it for you?

Are you using the G1 or G7 BC?

 

[treillw]

Is the velocity you are giving us supposed to be MV or velocity at each of those ranges?

What bullet are you using? Are you chronographing your loads or just trying to rely on the range finder to calculate it for you?

Are you using the G1 or G7 BC?

The velocities given for each data point is the "true muzzle velocity" calculated by the G7 program - tool used to find a best fit trajectory.

The bullet is a .308, 215 gn berger hybrid. I used G1.

The gun came from the smith with data entered into the G7 BR2 that was supposedly verified out to 1000 yards. When I take the gun to the range, I have to subtract 1 to 1.75 MOA from the corrections that the rangefinder is giving me. This is what he programmed into the rangefinder: Velocity = 2880, BC = .696 G1, Sight Height = 1.8"

I have no clue what velocity that is - whether its the true muzzle velocity, or what he tried to correct it to. Note that the BC is also different from what Berger advertises. Glad I paid $750 for drop data that is wrong!

 

[gohring3006]

Is the data that's entered using the same altitude as your current parameters?

 

[treillw]

Is the data that's entered using the same altitude as your current parameters?

The rangefinder measures the air pressure each time you range. I did not record the altitude and temperature when I was at the range collecting my own data - it is my understanding that altitude and temp is only used to calculate the air pressure, so it is irrelevant anyway. Is that correct?

 

[gohring3006]

The rangefinder measures the air pressure each time you range. I did not record the altitude and temperature when I was at the range collecting my own data - it is my understanding that altitude and temp is only used to calculate the air pressure, so it is irrelevant anyway. Is that correct?

Thinking about it, I believe you're right.
Did you try the G7 BC?

 

[treillw]

Thinking about it, I believe you're right.
Did you try the G7 BC?

No, I did not try using the alternate BC.

 

[gohring3006]

The rangefinder measures the air pressure each time you range. I did not record the altitude and temperature when I was at the range collecting my own data - it is my understanding that altitude and temp is only used to calculate the air pressure, so it is irrelevant anyway. Is that correct?

No, I did not try using the alternate BC.

It's a more refined ballistic calculation. Maybe it will help..

 

[treillw]

It's a more refined ballistic calculation. Maybe it will help..

I'll give it a shot. Thank you.

 

[WildRose]

My first reaction would be to contact the smith who set you up with it all. It seems that you have a problem with the inputs making accurate outputs near impossible.

 

[treillw]

My first reaction would be to contact the smith who set you up with it all. It seems that you have a problem with the inputs making accurate outputs near impossible.

Oh, there is definitely a problem and more than one!