Adjusting bc or velocity to match drop

[Joefrazell]

I shot out to 1150 yrds today with the 215 bergers at 2800 fps. The stated bc is .696 to match my actual drop I had to change the bc to .610. That put my horizontal at 32 moa which was perfect. It also worked at 705 yrds. Also I was shooting from the south to the north. You guys that have done this before, does that seem normal, to adjust the bc that much? I made sure my other atmospheric settings were correct. Also my scope has been through a tall target test and tracks correctly. Thanks! These are the 3 shots at 1150. The two upper are the ones after the correction.

 

[NEMTHunter]

What did you use to read velocity? I to am shooting about 2800 fps and the BC berger gave worked for me out to 800 yards. Infact I was hitting a little higher then it should have.

What is your twist?

Nice group by the way!

 

[gohring3006]

What elevation are you at? What twist?
I have seen this with 10 twist rifles at sea level.

 

[NEMTHunter]

I might add I am @2000 foot and have a 10 twist.

 

[Mercracing]

The general rule I follow is play with speed inside 800, BC after that.

 

[gohring3006]

The general rule I follow is play with speed inside 800, BC after that.

Agreed, 800 yards is not far enough to determine or adjust BC.

 

[26Reload]

The questions of today....
Is BC not determined by factory loaded and tested ammunition...
So the BC at one speed is not the same BC at another speed...
Like throwing rocks....when i could throw harder a rock of given weight might be faster and have a higher BC...
But now that my shoulder is crap and i can't hardly throw..the BC of the same rock would be considerably dissipated....

 

[Mercracing]

Correct. Berger gets a BC at a stated velocity. Faster and a higher BC. Slower and a lower BC. That also needs to be taken into account. I don't know what speed Berger is saying .696 but if it's faster then your going there's part of your BC drop.

 

[gohring3006]

Berger also revised its twist recommendation to 9 twist for the 215. We seen great accuracy, but the BC never worked out past 1000 yards in 10 twist. And when the temps dropped below 50 degrees it really fell apart. Again, at sea level.

 

[Joefrazell]

This is at 2400 ft elevation and I measured velocity with a magneto speed

 

[Joefrazell]

I know hornady with there bc's tell you to change depending on velocity and distance. Maybe it's the same with the bergers?

 

[Mercracing]

It's the same with everyone.

 

[gohring3006]

This is at 2400 ft elevation and I measured velocity with a magneto speed

Bergers twist calculator says your stabile at 1.57 Sg at 2400 ft elevation. Something else is wrong, maybe your getting extreme muzzle exit pressure, upsetting the bullet out of the gate.

 

[gohring3006]

Also, double check your inputs in your ballistic calculator.
Double check your humidity, scope height etc.
You could be adjusting BC because your impacts are lower due to wrong data inputs.