G1/G7 ballistic coefficient diffrences

[mapper]

Saw this thread, and it was informative..bc changes as a factor of velocity...
Some projectiles refrence it, others do not..

It was a decent read on page 2..
http://thefiringline.com/forums/showthread.php?t=555006&page=2

[Airgator0470]

Saw this thread, and it was informative..bc changes as a factor of velocity...
Some projectiles refrence it, others do not..

It was a decent read on page 2..
http://thefiringline.com/forums/showthread.php?t=555006&page=2

Some bullet makers offer BC's based off velocity.

[seadog]

Some bullet makers offer BC's based off velocity.

Yes, they shoot through two chronographs,one at the muzzle and one downrange.
Crunch the numbers then spit out an average.

I've read somewhere that the only true way to get accurate bc numbers is by doppler radar.

[0utlaw]

So we need to shoot at the giant golf ball at the airport? :dunno:

[seadog]

I believe the army has Doppler at Aberdeen testing grounds.

[Rumbler]

So does that TV station just North of I-10 on Thomasville road. :chinscratch:

[0utlaw]

ROADTRIP!!!

[mapper]

I have seen diffeent bc' based on velocity, seen where some people take a average of the bc then plug that in the drop charts.
Seen others only give 1 bc, and use muzzle velocity to run charts with..
Seen others use g7 data...
It is still an approximation..

[seadog]

I have seen diffeent bc' based on velocity, seen where some people take a average of the bc then plug that in the drop charts.
Seen others only give 1 bc, and use muzzle velocity to run charts with..
Seen others use g7 data...
It is still an approximation..

It really helps if you have the bc to velocity numbers for the bullet you are using.
Tell me what bullet you want to use and I will see if I have the numbers.

[seadog]

Here is an example.

Fps BCg1 BCg7
1500. 0.565. 0.314
2000. 0.629. 0.317
2500. 0.651. 0.327
3000. 0.678. 0.332

Those numbers are for Hornady .338 250gr BTHP Match.

And of course you probably already know this but I'll say it anyway.
G1 looks like a pistol bullet,flat base and rounded ogive.
G7 has a boat tail and a pointy ogive.
So G7 data reflects most modern bullet designs.

[seadog]

The problem I see with bullet manufacturers is that they don't give a shit because the mathematical models they use don't differentiate between bullet designs like wadcutter,flat base,spitzer,round nose semi Spitzer etc.etc.etc.

They assume one drag function and run with it.

G1&G7 just happen to be the most popular rounds that's why the data for G2,G5,G6,G8,GL is hard to come by.

[seadog]

Just figured I throw this simple graph in.

[Rumbler]

Interesting! Thanks!

I am going to guess that both peak in the 1000-1500 FPF range because if the turbulence during the sub to supersonic transition?

Is there any insight you can offer would be appreciated. Is there something else causing that spike in drag that you are aware of?

[seadog]

It's a shity,low resolution picture.

[seadog]

Two.

[mapper]

So,
To do a table right,
If a person had a list of g7 bc's at diffrent velocities, would they take an average of them, or use the one at the velocity/longest range they intend to shoot, providing the velocity is still supersonic,( mach 1.2 I think I saw somewhere) then verify by shots on targets at known ranges? Or put whatever bc is given either g1 or g7, and a measured muzzle velocity, and adjust from there, or are the diffrences not enough to be concerned with at NRA mid to long range distances...
I don't have anything capable of reaching farther than that..

Jbm ballistics has the g7 data in their library listed as (litz) otherwise it is g1 I think...
The bullet data base has some listed with velocities but does not make a distinction of which model it Is..

It may be a moot point with my shooting skills,or lack of, but I would like to know the proper way to derive a drop/driftc chart based on best available info..

Other wise I have been within reason and a couple clicks with a measured muzzle velocity, and a simple bc.. but that has been at short ranges

[seadog]

As you can see.

[mapper]

Ok, I see and understand...

If you had these pills.....
0.224 77 gr smk
O.224 80 gr smk

O.243 75 gr hornady v max
O.243 87 gr hornady v max

O.308 168 gr hornady match
0.308 175 gr smk

And measured muzzle velocity, what data would you use, and how would you build a drop/ drift chart?
All are diffrent length barrels with known twist rates..

Chrono data would be an average of 10 shots, more if need be, temperature, and wind readings recorded at muzzle, shots taken at 100 yds.

[seadog]

Three.

[mapper]

Good enough answer for me...
Just something I have always wanted to know..

[seadog]

And mapper, when I rest up and get sober,i'd like to continue this conversation.

[mapper]

Found this...about diffrent models..

http://www.sportingshootermag.com.au/news/bullet-ballistic-coefficients

http://www.frfrogspad.com/extbal.htm

Sounds good.....pause button engaged. :)

[Arclight]

Come on Arclight I know you can correct me at some point.
For what reason would I correct you?

[seadog]

Because im thinking you know a lot more than I do about this subject.

[Airgator0470]

So,
To do a table right,
If a person had a list of g7 bc's at diffrent velocities, would they take an average of them, or use the one at the velocity/longest range they intend to shoot, providing the velocity is still supersonic,( mach 1.2 I think I saw somewhere) then verify by shots on targets at known ranges? Or put whatever bc is given either g1 or g7, and a measured muzzle velocity, and adjust from there, or are the diffrences not enough to be concerned with at NRA mid to long range distances...
I don't have anything capable of reaching farther than that..

Jbm ballistics has the g7 data in their library listed as (litz) otherwise it is g1 I think...
The bullet data base has some listed with velocities but does not make a distinction of which model it Is..

It may be a moot point with my shooting skills,or lack of, but I would like to know the proper way to derive a drop/driftc chart based on best available info..

Other wise I have been within reason and a couple clicks with a measured muzzle velocity, and a simple bc.. but that has been at short ranges

Charles... I think you're making this more difficult than necessary... just start with either G1 or G7 at the muzzle and do the field work to fine tune.

Regardless of whether your initial chart is derived from using G1 or G7 BC's... you STILL will need to verify the end data AT THE RANGE. I've used G1 data for YEARS and in the past couple, G7... both are adequate to get close... and both require in the field data verification and fine tuning.

This thread reminds me of the debate years ago between a guy on Sniper's Hide and Brian Litz... lots of back and forth if I recall.

The best way to build a drop chart is to START at a given point... shoot to verify and fine tune, and then discover what YOUR rifle does with YOUR loads.

I don't have the data handy and can't find it... but I've seen charts developed with G1 data and G7 data and neither was significantly more precise than the other. It's the IN THE FIELD shooting and verification that matters in the end.

[mapper]

Bob,
I agree... it wasn't untill I saw the chart in the 2nd link I posted that showed the diffrences between them was not much..they both agreed with each other from 0- 600 yds then were within reason of each other further out..

I just never saw that before... so yes the diffrences are there, but not enough to be concerned with, as field data rules. And either one will get close enough.

[Airgator0470]

Bob,
I agree... it wasn't untill I saw the chart in the 2nd link I posted that showed the diffrences between them was not much..they both agreed with each other from 0- 600 yds then were within reason of each other further out..

I just never saw that before... so yes the diffrences are there, but not enough to be concerned with, as field data rules. And either one will get close enough.

One good thing about the shoot in April, is we will have the ability to get out past 500... the only problem is I'd like to shoot 10 rounds at 600, 700, 800, 90 and 1K and then go to the target and actually measure what's going on. A hit at those distances is simply "a hit"... unless you see where on the target the bullet struck, which is hard after the first 20 minutes of open range, you have little idea if it was a solid COM hit or a barely on the target hit... to me that's MOST IMPORTANT.

[Jafar]

Not to discredit anyone in this thread, because I have learned from reading it, but TRex has some great videos about this very subject on his YouTube channel.

[Airgator0470]

Not to discredit anyone in this thread, because I have learned from reading it, but TRex has some great videos about this very subject on his YouTube channel.

I love watching most of those videos...

[Airgator0470]

https://www.youtube.com/watch?v=gjzs79kDr6E

[seadog]

Note to self: don't post shit while drunk.

[Rumbler]

Note to self: don't post shit while drunk.

I wouldn't worry too much about it. I think some people either post only when they are drunk, or are drunk all the time. ;)

[Jafar]

Note to self: don't post shit while drunk.
I'm somehow cleared ten thousand posts while drunk. Step up your game hard charger.

[Rumbler]

See? Toldja. ;)

[0utlaw]

Note to self: don't post shit while drunk.

For some folks that would seriously limit the time available to post :yup: