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Question on bergers bc

 
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  #8  
Old 02-17-2009, 08:23 AM
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Re: Question on bergers bc

Mike,
You can just enter the average BC into the program.
If you enter a high BC that's only valid for the muzzle velocity, the program doesn't know to erode the BC as the bullet slows down. If you enter .644 at the muzzle velocity of 3300 fps, the program will apply .644 for the entire trajectory, which will be too high for most of the flight.
However, if you enter the average BC, it will be low for the first part of the trajectory when the bullet is fast, it will be very close to right on for much of the flight, and it will be a little high at the end of the flight. The net effect is that it will generate a trajectory that's much closer to reality than a BC that's only valid for muzzle velocity.

Sandman,
The G7 BC's for the 6.5mm 130 and 140 VLD's are: 0.282 and 0.304. These are valid for all flight speeds.
As to your question about the 6.5-284, go with the heavier bullets. Heavier bullets of similar shape will always be better performers at long range even though they suffer a depressed muzzle velocity. By the time they get to 1000 yards, they're faster than the lighter bullets that started out faster and lost velocity quickly. About the only count that light bullets beat heavy bullets is the flatness of the trajectory. This is only an issue if you don't have a rangefinder, and at long range, the heavy bullets end up flatter than the light ones anyway.

A word of caution about deriving BC from drop data...
If you're determining your drop at a given range by how much scope correction is needed at that range, you have to make sure your scope is calibrated, and you know how much each click is worth. In other words, many scopes that advertise 1/4 MOA clicks can actually move the crosshairs more or less than 1/4 MOA per click. If you think you've moved your crosshairs some amount at 700 yards, but they actually moved more or less than you think, your calculation of drop and BC will be inaccurate.

-Bryan
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And: Accuracy and Precision for Long Range Shooting

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  #9  
Old 02-17-2009, 10:38 PM
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Re: Question on bergers bc

This is for the berger boys I have bought thousands of dollars of your guys ammo . Do you guys not have a book out yet or a website where we can get the reloading info for your ammo .

It is a pain in the butt phoning all the time especially with my job as you are usually closed when I can phone . Cheers Jason
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  #10  
Old 02-18-2009, 02:48 AM
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Location: Utah
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Re: Question on bergers bc

Bryan and Kevin,

Thanks a bunch for being on here to answer our questions!
I would appreciate the g7 for the 30 cal 210.
Also, are these published somewhere? How do we get them for various bullets (yours and others)?

I thought exbal let you choose between g1 & g7. Is this not so??

Last edited by grit; 02-18-2009 at 03:09 AM.
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  #11  
Old 02-18-2009, 01:53 PM
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Re: Question on bergers bc

Jason,
I'm still getting the kinks worked out with my being added to the Berger email (again, the new kid) but you can email those requests in, instead of calling. There should be something in the works that will make those phone calls easier, too.

Once my email is up and running to speed, I should be able to handle the data requests and will be happy to do so.

Kevin Thomas
Berger Bullets
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  #12  
Old 02-18-2009, 02:11 PM
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Re: Question on bergers bc

Grit,
I'm going to defer to Bryan here, since he's the one dealing with the ballistics software, and is better qualified to answer this than I.

As far as getting the G7 BCs from other manufacturers, I doubt it. Virtually all US makers utilize the G1 model, simply to avoid confusion and allow a more direct comparison between the products. As shooters become more knowledgeable concerning BC, the makers will have a greater demand for BCs based on appropriate models that are better suited to the bullet in question, be it G1 through G7 or GL. With some of the computer programs out now, we're getting to that point, but as I said, Bryan's better qualified to answer this than I am.

Kevin Thomas
Berger Bullets
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  #13  
Old 02-18-2009, 02:25 PM
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Re: Question on bergers bc

Grit,
The G7 BC for the 30 cal 210 grain VLD is 0.315.

I don't own exbal, so I don't know if it can accept G7 BC's or not.
Here's a link to a very good (free online) ballistics program that lets you use G7 BC's:
http://www.eskimo.com/~jbm/calculations/traj/traj.html

Just enter your conditions and be sure to select G7 if you input the 0.315 BC for the 210 VLD. If you don't tell the program you're giving it a G7 BC it will assume you're giving it the 'ol G1 and it will produce useless results. The output of this program is quite accurate if it's given good input.

There is currently no resource available to get G7 BC's from all brands. As Kevin said, it will be an uphill fight to get most of the other bullet makers to convert. We're working on materials that are designed to bring the G7 referenced BC's into the mainstream. In the mean time, I'm happy to continue providing G7 BC's for Berger bullets on request.

-Bryan
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Author of: Applied Ballistics for Long Range Shooting
And: Accuracy and Precision for Long Range Shooting

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  #14  
Old 02-18-2009, 05:00 PM
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Location: Utah
Posts: 1,377
Re: Question on bergers bc

Thanks.

I don't want to take advantage of your time. But I have a few more questions.

I ran the numbers for the 6.5 140 at 2600 fps using the g1 and g7 models. The numbers to 1k were virtually identical.

Can you illustrate the differences in using the two models. I will get specific. I am shooting the 210's at 3013 fps. Max range 1500 ish.
Alt, 5000'
pressure at altitude, 25.4"
temp, 50
humidity, 24%

Next question, I don't see an option to use the g7 on my Nightforce xbal software. I thought it had it.
However, The program offers the option to define multiple bc's at certain velocities.

For example, if I choose the 308 175 Smk the program shows two columns. Looks like this:

BC - Lower velocity limits
.505- 2800 fps
.496 - 1800 fps
.485 - 0 fps


Now, when I choose your 210 it looks like this:

BC - Lower limit
.616 - 0 fps


Perhaps you could provide me with bc's at lower limits like above to better utilize the program I have??

If the G7 model or others are more accurate, I am all for switching. In the mean time, I'd like to use what I have as accurately as possible.

Thanks again for your time!
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