Is it reasonable to think two different projectiles weighing different amounts 123gr lapua scenar and 130gr norma diamond line that share a BC of .547 would follow the same G7 flight path if fired at from the same rifle at the same velocity ?
Range Report same BC different weight
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Re: same BC different weight
bet my 158 grain .357 has a lower BC than both your Norma and Lapua. Goes to show that weight is not everything.
bet my 158 grain .357 has a lower BC than both your Norma and Lapua. Goes to show that weight is not everything.
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ch'e</div><div class="ubbcode-body">Is it reasonable to think two different projectiles weighing different amounts 123gr lapua scenar and 130gr norma diamond line that share a BC of .547 would follow the same G7 flight path if fired at from the same rifle at the same velocity ? </div></div>
That's an interesting question. My first instinct is to say that yes they should have similar trajectories all else being equal. However, the BC for each will be the product of different components and that may make a difference at longer ranges. I trust both bullets are the same caliber, so that the Lapua will have a lower sectional density compared to the Norma, but makes it up with a more aerodynamic shape.
On the other hand, the BC value of a bullet varies depending on the velocity at which it travels, which is why the G7 is used so as to address this variability. A G7 value of .547 seems rather high so I suspect that is a G1 value and thus subject to change. Also, Lapua and Norma may have different methods of calculating their claimed BC values and one or both may be off in real life.
Good question.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ch'e</div><div class="ubbcode-body">Is it reasonable to think two different projectiles weighing different amounts 123gr lapua scenar and 130gr norma diamond line that share a BC of .547 would follow the same G7 flight path if fired at from the same rifle at the same velocity ? </div></div>
That's an interesting question. My first instinct is to say that yes they should have similar trajectories all else being equal. However, the BC for each will be the product of different components and that may make a difference at longer ranges. I trust both bullets are the same caliber, so that the Lapua will have a lower sectional density compared to the Norma, but makes it up with a more aerodynamic shape.
On the other hand, the BC value of a bullet varies depending on the velocity at which it travels, which is why the G7 is used so as to address this variability. A G7 value of .547 seems rather high so I suspect that is a G1 value and thus subject to change. Also, Lapua and Norma may have different methods of calculating their claimed BC values and one or both may be off in real life.
Good question.
Re: same BC different weight
Yes , the .547 is a G1 BC. Interesting , I put the same G1 inputs into Pejsa and changed out the 6.5 projectiles and the MOA didn't alter only the impact energy .I haven't tried other programs using the G7 BC's as I don't know them .
Yes , the .547 is a G1 BC. Interesting , I put the same G1 inputs into Pejsa and changed out the 6.5 projectiles and the MOA didn't alter only the impact energy .I haven't tried other programs using the G7 BC's as I don't know them .
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattj</div><div class="ubbcode-body">JBM has G7 BCs if you choose the bullet in the drop-down. </div></div>
I looked in the drop down in the trajectory but I cant see g7 bc numbers there --have you seen them ? if so can you direct me to them please .cheers
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattj</div><div class="ubbcode-body">JBM has G7 BCs if you choose the bullet in the drop-down. </div></div>
I looked in the drop down in the trajectory but I cant see g7 bc numbers there --have you seen them ? if so can you direct me to them please .cheers
Re: same BC different weight
What Mattj was talking about is using the listing for the bullets you are studying, where the name (Litz) appears. This is in honor of Bryan Litz who has been doing a lot of work in this area, straightening out these BC issues. The bullets you mention do not have a listing with (Litz) and there is only one listing for any Norma bullet.
Pejsa will not know how to change the G1 BC,(how could it?) and so the trajectory will be the same. About the only way would be to test them out and calculate the BC yourself.
What Mattj was talking about is using the listing for the bullets you are studying, where the name (Litz) appears. This is in honor of Bryan Litz who has been doing a lot of work in this area, straightening out these BC issues. The bullets you mention do not have a listing with (Litz) and there is only one listing for any Norma bullet.
Pejsa will not know how to change the G1 BC,(how could it?) and so the trajectory will be the same. About the only way would be to test them out and calculate the BC yourself.
Re: same BC different weight
I have the Iphone with Ballistic FTE and the Lapua program with the doppler raydar drop for their 123gr scenar on my desk top .For me to match the 123gr scanar flight path on my iphone with the norma 130gr I caculate the G7 to be .261g7 bc providing they do actually fly the same .One other thing I am thinking though is each program has it own formulae and each might show a slightly different BC number because of this .I have to go to my NRA range and let them fly at all the ranges and confirm the caculations .
I have the Iphone with Ballistic FTE and the Lapua program with the doppler raydar drop for their 123gr scenar on my desk top .For me to match the 123gr scanar flight path on my iphone with the norma 130gr I caculate the G7 to be .261g7 bc providing they do actually fly the same .One other thing I am thinking though is each program has it own formulae and each might show a slightly different BC number because of this .I have to go to my NRA range and let them fly at all the ranges and confirm the caculations .
Re: same BC different weight
I took two bullets that Litz measured (165 gr. A-max and 155 gr. PMP) that had the same G7 BC and entered every detail into JBM, including bullet length and accounting for spin drift. The trajectories were almost identical for both drop and wind. The 165 gr. bullet had more energy, as you would expect (631 ft./lbs @ 1000 vs. 593. Obviously that would be of some value to a big-game hunter but the 165 would have more recoil. And, in practice, you'd either A) drive the 155 higher or B) not be able to drive the 165 as high.
Re: different programs. Each probably does have its own variation on the known ballistics formulas. Litz' program comes very close to JBM (but doesn't presently account for spin drift). Since you have Ballistic, I recommend setting it to use the JBM engine. Then, if you use JBM on your desktop, you'll be working with the same algorithms all the time.
I took two bullets that Litz measured (165 gr. A-max and 155 gr. PMP) that had the same G7 BC and entered every detail into JBM, including bullet length and accounting for spin drift. The trajectories were almost identical for both drop and wind. The 165 gr. bullet had more energy, as you would expect (631 ft./lbs @ 1000 vs. 593. Obviously that would be of some value to a big-game hunter but the 165 would have more recoil. And, in practice, you'd either A) drive the 155 higher or B) not be able to drive the 165 as high.
Re: different programs. Each probably does have its own variation on the known ballistics formulas. Litz' program comes very close to JBM (but doesn't presently account for spin drift). Since you have Ballistic, I recommend setting it to use the JBM engine. Then, if you use JBM on your desktop, you'll be working with the same algorithms all the time.
Re: same BC different weight
Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it.
But, to quote Bryan Litz, JBM Ballistics is the gold standard in ballistics programs.
And Bryan's book has a good short algorithm for estimating spindrift, for those who are concerned about it.
http://www.appliedballisticsllc.com/
Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it.
But, to quote Bryan Litz, JBM Ballistics is the gold standard in ballistics programs.
And Bryan's book has a good short algorithm for estimating spindrift, for those who are concerned about it.
http://www.appliedballisticsllc.com/
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it.</div></div>
Actually PCs have come a long way in the last 10-15 years. I have written and run 6DOF programs on PCs and they are quite fast. The problem I have with them is getting reliable coefficients -- without that, they just aren't that useful to me.
You can get good drift estimates with a modified point mass program which requires fewer coefficients.
Since drift is a small correction to the trajectory, I think approximate methods like Bryan Litz' formula coupled with Don Miller's stability formula are very useful.
As far as the different weights with same BC -- they should have the same trajectory. The weight is in the BC since the BC = sectional density / form factor. Form factor is just the ratio of the drag function CD to the bullet CD. You can see the formulas here:
Sectional Density Topic
Brad
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it.</div></div>
Actually PCs have come a long way in the last 10-15 years. I have written and run 6DOF programs on PCs and they are quite fast. The problem I have with them is getting reliable coefficients -- without that, they just aren't that useful to me.
You can get good drift estimates with a modified point mass program which requires fewer coefficients.
Since drift is a small correction to the trajectory, I think approximate methods like Bryan Litz' formula coupled with Don Miller's stability formula are very useful.
As far as the different weights with same BC -- they should have the same trajectory. The weight is in the BC since the BC = sectional density / form factor. Form factor is just the ratio of the drag function CD to the bullet CD. You can see the formulas here:
Sectional Density Topic
Brad
Re: same BC different weight
Just an overall observation about SH:
Often there are ridiculous threads that just degenerate into foul-mouthed name calling and accusations. Then there are threads where experts like Lindy, Brad or Bryan chime in. We are fortunate to have their insight and experience.
Just an overall observation about SH:
Often there are ridiculous threads that just degenerate into foul-mouthed name calling and accusations. Then there are threads where experts like Lindy, Brad or Bryan chime in. We are fortunate to have their insight and experience.
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The problem I have with them is getting reliable coefficients...</div></div>
By which I assume you mean the drag coefficients. We just need to take up a collection to get you a doppler radar.
I don't worry too much about spin drift. Given the other sources of ballistic program uncertainties which accompany a trajectory calculation, I think your program does a splendid job.
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The problem I have with them is getting reliable coefficients...</div></div>
By which I assume you mean the drag coefficients. We just need to take up a collection to get you a doppler radar.
I don't worry too much about spin drift. Given the other sources of ballistic program uncertainties which accompany a trajectory calculation, I think your program does a splendid job.
Re: same BC different weight
I gotta say I think were all very lucky to have the collective intelligence of guys like Lindy,Bryan Litz and now Mr JBM helping us to further our knowledge of what once was a great black hole to most--thank you !!
I gotta say I think were all very lucky to have the collective intelligence of guys like Lindy,Bryan Litz and now Mr JBM helping us to further our knowledge of what once was a great black hole to most--thank you !!
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it. </div></div>
You need to start considering upgrading your Pentium II running Windows 98.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Programs which are not six degree of freedom ballistic programs, which run on mainframes because PCs mostly haven't got the computing power to run them, don't try to calculate spindrift. They just estimate it. </div></div>
You need to start considering upgrading your Pentium II running Windows 98.
Re: same BC different weight
Well, I have.
But I don't have a 6DOF ballistics program. If someone would like to direct me to one which will run on a P.C., I'd be pleased to run it.
Well, I have.
But I don't have a 6DOF ballistics program. If someone would like to direct me to one which will run on a P.C., I'd be pleased to run it.
Re: same BC different weight
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">
By which I assume you mean the drag coefficients. We just need to take up a collection to get you a doppler radar.
</div></div>
The drag coefficient we can get pretty accurately from some projectiles, it's the coefficients like lift force coefficient, Magnus coefficients, Spin damping coefficients, etc. They are all dependent on mach number and just don't exist. I have talked to people that do Computational Fluid Dynamics about modeling them, but the accuracy wasn't there.
I'm guessing Bryan knows a lot more about this than I do -- I think that's more his field.
Brad
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">
By which I assume you mean the drag coefficients. We just need to take up a collection to get you a doppler radar.
</div></div>
The drag coefficient we can get pretty accurately from some projectiles, it's the coefficients like lift force coefficient, Magnus coefficients, Spin damping coefficients, etc. They are all dependent on mach number and just don't exist. I have talked to people that do Computational Fluid Dynamics about modeling them, but the accuracy wasn't there.
I'm guessing Bryan knows a lot more about this than I do -- I think that's more his field.
Brad
Re: same BC different weight
Why do I get the feeling that we are measuring with a laser something we will be cutting with an ax? At some point, infinitesimal calculations have some diminishing value in ballistics.
Why do I get the feeling that we are measuring with a laser something we will be cutting with an ax? At some point, infinitesimal calculations have some diminishing value in ballistics.
Re: same BC different weight
Well, and all that ballistic program accuracy will avail one nought if one slaps the frickin' trigger.
I mostly miss shots from dicking up one of the fundamentals of marksmanship rather than the dope.
Well, and all that ballistic program accuracy will avail one nought if one slaps the frickin' trigger.
I mostly miss shots from dicking up one of the fundamentals of marksmanship rather than the dope.
Re: same BC different weight
It's true that we have to do our part to hit targets. However, just because we're all not 'perfect' marksman doesn't justify working with compromised data.
If you do an accurate, thorough job with the ballistics (as Brad has enabled us to do with his tools) you at least have the best potential to hit the target <span style="font-style: italic">if</span> you get everything else right. I for one don't go out the door planning to F something up. The point is to at least try to do everything right from predicting the trajectory to executing the shot. If you fall short, you know where improvement is required. Given the tools we have available, there's no excuse for not getting the ballistics right.
Re: Aero Coefficients.
The ones Brad mentioned (pitching moment, Magnus force and moment, damping derivatives, etc) these are the hardest to measure. They are the hardest to measure because they're so subtle. Because they're so subtle, they have small effects (making them hard to measure
). The dominant forces are gravity (well known) and drag. Seeing has how drag is such a dominant force, that coefficient is relatively easy to measure with accuracy. Furthermore, getting it right enables the most important part of the trajectory analysis to be accurate. In other words, <span style="text-decoration: underline">'things' that are easy to measure are so because their effects are most apparent, and vise versa</span>.
-Bryan
It's true that we have to do our part to hit targets. However, just because we're all not 'perfect' marksman doesn't justify working with compromised data.
If you do an accurate, thorough job with the ballistics (as Brad has enabled us to do with his tools) you at least have the best potential to hit the target <span style="font-style: italic">if</span> you get everything else right. I for one don't go out the door planning to F something up. The point is to at least try to do everything right from predicting the trajectory to executing the shot. If you fall short, you know where improvement is required. Given the tools we have available, there's no excuse for not getting the ballistics right.
Re: Aero Coefficients.
The ones Brad mentioned (pitching moment, Magnus force and moment, damping derivatives, etc) these are the hardest to measure. They are the hardest to measure because they're so subtle. Because they're so subtle, they have small effects (making them hard to measure
-Bryan
Re: same BC different weight
Thank you Brad for an AWESOME website that I can't leave alone! Thank you Bryan Litz for all the work you do in this industry to make it possible for someone with as little knowledge as myself to go out and have a chance to actually hit what I'm aiming at when I do my part! Preshate ya'll!
Michael T.
Thank you Brad for an AWESOME website that I can't leave alone! Thank you Bryan Litz for all the work you do in this industry to make it possible for someone with as little knowledge as myself to go out and have a chance to actually hit what I'm aiming at when I do my part! Preshate ya'll!
Michael T.
