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English Mike Super Member
Joined: Jan 08, 2007 Posts: 1709 Location: Whitehaven, Cumbria, UK
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Posted: Sat Sep 02, 2017 5:18 pm Post subject: Ballistic Coefficient |
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I note that several manufacturers are now giving two differing figures for a bullet's BC: G1 & G7.
Berger is one & they have an explanation here that makes a lot of sense.
My question is: Will this affect the accuracy of trajectory projections when using PointBlank?
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Elvis Super Member
Joined: Jul 27, 2008 Posts: 9239 Location: south island New Zealand
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Posted: Sat Sep 02, 2017 5:42 pm Post subject: Re: Ballistic Coefficient |
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there is also different figures for different speeds......you can end up chasing your tail if shooting really long as figure will change as speed drops.
aim and shoot . dont try for range of more than say 350 yards and its all just gobbledegook anyway LOL.
_________________ You shot it You pluck it !
Them who eats the most duck eats the most feathers! |
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sat Sep 02, 2017 6:54 pm Post subject: Re: Ballistic Coefficient |
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English Mike, what bullet are you trying to use? I've done some BC testing to check between actual and advertising.
www.huntingnut.com/ind...=ballistic
For those not familiar with G7, it is better optimized for modern low-drag bullets. G1 and G7 are distinctly different values and require different algorithms to generate trajectories.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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English Mike Super Member
Joined: Jan 08, 2007 Posts: 1709 Location: Whitehaven, Cumbria, UK
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Posted: Sun Sep 03, 2017 4:54 pm Post subject: Re: Ballistic Coefficient |
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slimjim wrote: |
English Mike, what bullet are you trying to use? I've done some BC testing to check between actual and advertising.
www.huntingnut.com/ind...=ballistic
For those not familiar with G7, it is better optimized for modern low-drag bullets. G1 and G7 are distinctly different values and require different algorithms to generate trajectories. |
Moly coated .243 Lapua Scenar 90gr which definitely resemble the G7 profile (boat tail, long ogive, open tip).
Using the G7 profile gives a lower BC than the G1, which confuses the heck out of me.
ETA I just read through all the posts in your link & that helps a great deal.
I have at least 10 different varieties of .277 bullets sitting in Albuquerque if you ever want any more to play with, though I can't tell you what exactly for another eight weeks, which is how long it'll be till I'm out there again.
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Sun Sep 03, 2017 7:05 pm Post subject: Re: Ballistic Coefficient |
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English Mike wrote: |
Using the G7 profile gives a lower BC than the G1, which confuses the heck out of me. |
The G7 BC can't be used in typical ballistic calculators designed for G1 inputs. I don't know if PointBlank handles G7 BCs? If it doesn't I would use the calculator on the Berger or Applied Ballistics websites. They are compatible with G7 inputs.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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Vince Site Admin
Joined: May 25, 2005 Posts: 15704 Location: Brisbane AUSTRALIA
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Posted: Sun Sep 03, 2017 8:13 pm Post subject: Re: Ballistic Coefficient |
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Mike, unless you are looking for Bench Rest accuracy I tend to agree with Elvis. Pick a projectile that you think will meet your needs and try it out. If it doesn't perform as you hoped, or you can't find a load that works, then look at a different projectile.
I love what Slim does with his testing, but it goes beyond anything I will ever need or do, however it 'scratches an itch' that Slim needs to scratch, and that's great. I think that with the multitude of different projectiles on the market today, the average shooter/hunter gets confused and too wrapped around the axles with advertised claims. Said shooter then gets discouraged when they don't always achieve those claims.
I look at my target species, look at a type (HP, SP etc) and weight of projectile to humanely harvest that species then develop a load that will give me minute of critter. Anything beyond that, I find, creates confusion leading to not trusting your loads.
_________________ Cheers, Vince
Illegitimi non carborundum
(Never let the bastards grind you down)
Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God.
"Nulla Si Fa Senza Volonta."
(Without Commitment, Nothing Gets Done) |
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Elvis Super Member
Joined: Jul 27, 2008 Posts: 9239 Location: south island New Zealand
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DallanC Site Admin
Joined: Jan 18, 2005 Posts: 3571 Location: Utah
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Posted: Tue Sep 05, 2017 12:17 pm Post subject: Re: Ballistic Coefficient |
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PointBlank is based on a G1 table. I've rarely had people ask for G7 based computation, but not enough to justify the work to implement it.
Plus.... Sierra uses THREE different BC's for their bullets, depending on the velocity range you shoot them in. Its all pretty technical, all a Ballistics Calculator helps with is giving a representation for a theoretical trajectory.
-DallanC
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Vince Site Admin
Joined: May 25, 2005 Posts: 15704 Location: Brisbane AUSTRALIA
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Posted: Tue Sep 05, 2017 3:56 pm Post subject: Re: Ballistic Coefficient |
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_________________ Cheers, Vince
Illegitimi non carborundum
(Never let the bastards grind you down)
Live simply. Love generously. Care deeply. Speak kindly. Leave the rest to God.
"Nulla Si Fa Senza Volonta."
(Without Commitment, Nothing Gets Done) |
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slimjim Super Member
Joined: May 16, 2009 Posts: 8314 Location: Fort Worth TX
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Posted: Wed Sep 06, 2017 6:01 pm Post subject: Re: Ballistic Coefficient |
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DallanC wrote: |
Sierra uses THREE different BC's for their bullets, depending on the velocity range you shoot them in. |
During my BC testing I found several bullets whose BC (G1) noticeably changed when tested at different speeds. It appropriate for the bullet, a G7 BC provides better drag/trajectory calculations over the more significant velocity change associated with long range shooting.
_________________ "To anger a conservative, lie to him. To anger a liberal, tell him the truth." - Theodore Roosevelt
"The world is a dangerous place to live; not because of the people who are evil, but because of the people who don't do anything about it." - Albert Einstein |
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DallanC Site Admin
Joined: Jan 18, 2005 Posts: 3571 Location: Utah
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Posted: Wed Sep 06, 2017 9:34 pm Post subject: Re: Ballistic Coefficient |
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Yea, the big problem is most mfgs dont give out a G7 based SD for their bullets. Everyone is too used to G1 values.
-DallanC
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English Mike Super Member
Joined: Jan 08, 2007 Posts: 1709 Location: Whitehaven, Cumbria, UK
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