Range Report Truing BC...how much?

[cecztayl]

When truing BC, how much adjustment is too much when adjusting the BC.

6.5x47
140 eld-m @ 2766 FPS. (Labradar)
ES= 8
SD= 3.3

Shot from 200-1k

From 600 & 700 I had to add about .2
From 800-1k I had to add about .3

To match up my calculator to my actual impacts I adjusted the BC from .646 (advertised) too .590.

Everything lines up perfect but it just seems that that was a lot of adjustment.

What are your thoughts?

 

[morganlamprecht]

ive only ran the g7, but ive never had to adjust more than .300-.310 for 2700-2800 fps

could be slight tracking or ranging errors?

 

[Lowlight]

looks right you are going slow,

A 6.5 is meant for 2850, you are below that hence the change.

It's a little bigger than normal and you might have something else in there affecting it, but it's not that far off the mark.


SD has no bearing on it, just velocity, then Barre! Type and internal Specs.

 

[cecztayl]

Thanks guys! The numbers lined up perfect. I was just second guessing because it seemed excessive.

I pulled atmospherics from weather flow weather meter and in the past this has been spot on so I trust the system.

@Lowlight thanks for the confirmation!

I will verify everything this weekend or next to see if all holds true.

 

[cecztayl]

@morganlamprecht the range was confirmed with 2 different rangefinders. So I feel confident about the range.

The only thing I don’t have figured was a very, very slight downward angle to the targets from firing position....very slight.

 

[Rob01]

Did you run a full tracking test on the scope? That can sometimes catch people who think it's the load.

Also did you try the Hornady 4Dof program? If not try it and see how it works. I have used it with that bullets and it's dead on to 1250 yards.

 

[Lowlight]

Hornady works because their BC is already trued to 800 yards...

So the numbers being used by Hornady tend to be better from the start.

For other programs you can go to the Hornady website and they have 3 different values, picking the right one could help. I have done this with the Valkyrie stuff, using other software. The middle value is best in my case, which is slightly lower.

 

[Rob01]

Actually taking the three numbers and using the average works well too.

The 4Dof uses their custom curves and if using the ELDs it's really the best way to go.

 

[FishDr]

I used all three of the Hornady numbers and set them up as a “banded” BC for their ELD-m bullet. Seemed to work as far out as I could get on the initial range trip which was ab 800 yards. Will this data hold past that? Always willing to learn a better way.

 

[Lowlight]

You can band it,

that will work well as long as your software can handled banded BCs

 

[FishDr]

Thanks Frank. Appreciate the confirmation.

 

[cecztayl]

@Rob01 i have not sat down and ran a full tracking test on this scope ( G2 razor) but it has ran true to 1200 with other bullets with very slight tweaking on the BC.

Also I have the 4dof program and will run the numbers in it and see how they compare to what I have now in ballistic arc.

I feel pretty confident now. Just was questioning how much I had to adjust the BC initially.

Thanks for all the replies fellas!

 

[Rob01]

I bet the 4Dof will be very close. Let us know.

 

[cecztayl]

So, just updated atmospherics & rifle info in 4dof.

The only thing I didn’t change was the form factor which if memory serves correctly I had played with that in the past.

Everything matched my trued dope in ballistic arc out to 800.

900 was giving .2 more than actual
1k was giving .3 more than actual.

This could be from the form factor change previously made.

Pretty close regardless!

 

[Notdylan]

Do the custom drag models in AB need to be trued or is that already handled for you? Even if you're running lower velocities?