Ballistic coefficient G1 and G7

[CoryT]

Re: Ballistic coefficient G1 and G7

While an argument might be made that the G7 BC might be a more valid model on which to base trajectory predictions, it does not seem that the theoretical differance tracks into reality. Programs using G1 with either Pejsa's DK system or banded G1 numbers seem to provide perfectly usable solutions, well within total system error. While I would not turn down a G7 based system (that calculated a usable solution), neither am I driven to pursue a change from the G1 based system I currently use.

Since we cannot actually KNOW, to any degree of precision the ACTUAL velocity of a shot we are about to fire, plus the measurement error in the environmental conditions, range / angle precision margins, shooter error, sight adjustment error, not to mention the ability of the shooter to hold, whatever differance there may be between the two BC solutions does not seem to be a practical differance.

EVERY system I've ever seen come through class has required some sort of 'tuning' to get it to provide a usable solution at 1000+ meters. It would seem that that ability to adjust the curve, based on observed reality, is more important than the method or basis itself.

Bryan would seem to be factually correct in stating the G7 tracks better, at least using his test systems and computer models of each one. However, it does not seem to me that that differance is causing a problem with a properly tuned system in the field. What would be ideal is a field usable system that did not REQUIRE any 'tuning', but I have yet to see anything like that actually work. If one DID, I would not be suprised if it was G7 based.

 

[MALLARD]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">
Here is data straight from JBM with your G7

Here is the same exact data with G1

</div></div><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">
You also missed the part about having every program available, as well as calibrating my software and shooting. </div></div>

LL,
im sorry if this question has already been addressed

Between the G1 and G7 jbm shows 1 moa difference at 1100y, you also mention using more then one ballisitics program.

so my question, lets say one program says the difference between the g1 and g7 is 5 moa, and a different program says the difference between the g1 and g7 is 7 moa. ( im just throwing numbers out there)

What do you dial as your actual firing solution ? do you take an average of the numbers ? or just stick with one of the outputs ?

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

I stick with one,

As I wrote earlier if I have immediate access to G7, I tend to use that, however my go to program works better with G1, so when I am not just crunching numbers for my own enjoyment I use the more readily available G1 so I am not hunting for the G7. But with apps on the fly, I can usually find the G7 pretty easily.

FFS and LB3 is what is loaded on my NOMAD and for both G1 works 100% But as mentioned they model different than the rest, and appear to be doing a good job at it.

I don't sample programs and solutions in the field, that is a waste of time. You can just as easily calibrate and true the program than going through the trouble to sample each one. And as you can see, they should not be off by so much, I have never noticed a 5 MOA difference that wasn't an input error of some kind. If the program was giving me such a big swing I would toss it to the side and never use it. Where did see a problem that was 4 MOA was with Bulletflight beyond 1500, it was dead on up until we inputted 1500m in the system and then it threw everything off by 1 Mil. That immediately got it tossed to the worthless pile for field use. Two of us side by side saw this same thing, with two different iPhones.

 

[ctressler]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body">Has anyone had any experience with the Apple application , JBM Ballistic FTE . I can't seem to find anyway to save a custom bullets BC and velocity data. The supplier of the application does not return any contact .
I spoke to the apple shop in my area and they did not even know the app existed. Great service! </div></div>

Save your calculated output as a favorite and then you can recall that favorite back into the solver. There is no way to update the internal library of BC data.

 

[KYpatriot]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CoryT</div><div class="ubbcode-body">While an argument might be made that the G7 BC might be a more valid model on which to base trajectory predictions, it does not seem that the theoretical differance tracks into reality. Programs using G1 with either Pejsa's DK system or banded G1 numbers seem to provide perfectly usable solutions, well within total system error. While I would not turn down a G7 based system (that calculated a usable solution), neither am I driven to pursue a change from the G1 based system I currently use.

Since we cannot actually KNOW, to any degree of precision the ACTUAL velocity of a shot we are about to fire, plus the measurement error in the environmental conditions, range / angle precision margins, shooter error, sight adjustment error, not to mention the ability of the shooter to hold, whatever differance there may be between the two BC solutions does not seem to be a practical differance.

EVERY system I've ever seen come through class has required some sort of 'tuning' to get it to provide a usable solution at 1000+ meters. It would seem that that ability to adjust the curve, based on observed reality, is more important than the method or basis itself.

Bryan would seem to be factually correct in stating the G7 tracks better, at least using his test systems and computer models of each one. However, it does not seem to me that that differance is causing a problem with a properly tuned system in the field. What would be ideal is a field usable system that did not REQUIRE any 'tuning', but I have yet to see anything like that actually work. If one DID, I would not be suprised if it was G7 based.</div></div>

Well said Cory... you said what I was trying to convey much more clearly than I was able. If these programs fine tuned their algorithms using data collected from environmentally controlled long range shots fired from test barrels mounted in a fixture then the only variable left would be variation in bullet construction. Then we would have what you are seeking, a program that would require very little or even no adjustment in the field--a near perfect ballistics computer.

The obvious problem is finding such an location to gather the data to tweak the algorithms. I suspect the opportunity exists somewhere. You are basically doing the same thing when you true the program in the field, but it would be more accurate and repeatable if the conditions were more controlled.

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Mister Ouchie</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body">Has anyone had any experience with the Apple application , JBM Ballistic FTE . I can't seem to find anyway to save a custom bullets BC and velocity data. The supplier of the application does not return any contact .
I spoke to the apple shop in my area and they did not even know the app existed. Great service! </div></div>

Once you calc the trajectory you can save it as a "favorite" (upper right button I think).</div></div>
Ok thanks for that but I was actually wanting to save the actual custom bullet data so it can be accessed like one of the library bullets can be. I don't use factory ammo or factory bullets , so a library of factory bullets is of no value to me.
I guess it can't do it but I was not sure I was doing it right.
If I save the trajectory can I reload it later and then apply changed atmospheric details to it ?

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CTressler</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Country</div><div class="ubbcode-body">Has anyone had any experience with the Apple application , JBM Ballistic FTE . I can't seem to find anyway to save a custom bullets BC and velocity data. The supplier of the application does not return any contact .
I spoke to the apple shop in my area and they did not even know the app existed. Great service! </div></div>

Save your calculated output as a favorite and then you can recall that favorite back into the solver. There is no way to update the internal library of BC data.</div></div>

That is a huge pity for me. The advertising clearly said abilty to " CREATE CUSTOM BULLET " why would you want to enter all that BC and velocity data and not be able to save it also as a stand alone custom bullet in memory . Annoying .

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: longdistance</div><div class="ubbcode-body">anyone have experiance with the sierra extieror ballistics program, cd rom? </div></div>
have used Sierra infinity for a while but again no ability to create and save my custom bullet . Worked ok with my mates sierra bullets as the Sierra library has stepped BC's but the other brands don't so it was no real use to me.
What do you wnat to know? I may be able to help if I can.

 

[KYpatriot]

Re: Ballistic coefficient G1 and G7

Country try Shooter...it is not much money and you can create and save ammo characteristics.

 

[hooksz86]

Re: Ballistic coefficient G1 and G7

ya, I found that out today on the stepped bc's today. I didnt think about changing the info on the manufacture bullets. But ya they dont have the stepped numbers for the other brands, such as berger. I called and talked to a guy from sierra about it. It was kinda funny when I was asking him about G7 and entering in a custom burger bullet. But I did do some compairing with it. If i leave the BC at .768 and FPS at 2756 for the 300 SMK it only varies around 4inches off at 1800yards between doing it that way and using the step down. and that is 1-5 BC .768, .760, .750, .750, 750 and velocity ranges 1-4 muzzle to 2300, 2300 to 1800, and 1800 below. So anyway I guess if im going to try out the G7 to compair to G1 for my self I need to get a program that works good with G7. Do you know a good one that doesnt cost a lot.

And I didnt know it was going to get this indepth with this topic. For me I just want to get in the ball park at 1500 to 2200 yards. And then half the fun and good shooting experiance comes from correcting your shot from 1st to 2nd shot. For me, I dont have the money to buy a range finder to figure out a real life scenario target distance that exact to be that exact with a program anyway. And if im at a range weather its at my house or at raton I will then know the distance for sure and can use a programe though, then it would be very good for a 1st round hit for scoring reasions in competition.

Hey <span style="font-style: italic"><span style="text-decoration: underline">Brian</span></span>,

Can you give us the step down G1 BC's of the 338, 300 berger and its velocety boundries for those G1 BC's so that I can use it better in my programe that I have. I promis I will get a programe for G7 and use it also.lol

And dont worry, I will always keep buying Berger Bullets.

When is berger going to make a VLD hunting bullet in .338, 300gr HPBT? You know, for a nice mile long shot on a black bear or elk and have a nice mushroom expansion.

Dont take me the wrong way though, I think it is awsome to be able to punch in some #'s and pull triger and make a first round hit. I learned a lot about ballistics and ballistic programs from this topic. And on the few post of hy jacking the topic, I did not feel that anyone got off topic at all. <span style="text-decoration: underline">A good debate always makes for a better outcome.</span>

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CTressler</div><div class="ubbcode-body">LL, You said it yourself, your a shooter not a scientist yet you wax on like you know it all. Did it occur to you that my post was for the original poster of this thread, which you have highjacked.</div></div>

Want to clarify something, so not to think I am just being a dick for the sake being argumentative with Bryan. <span style="font-style: italic">(A charge many like to levy)</span> I certainly respect everything he has done, but to the question of me "waxing on like a know it all" well I want to bring your attention to a review written, that sort of says the same thing I have, as well as others.

<span style="text-decoration: underline">Understand I had not read this until tonight, but you'll see some familiar themes.</span>

You can read it in it's entirety here:

http://www.longrangehunting.com/articles/book-review-applied-ballistics-long-range-shooting-1.php (Sep/2009)

A few notable lines to go towards my debate with Bryan:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">A central subject of the book is the proposed use of the G7 drag model instead of the usual and widely available G1 function. While the general use of G7 (first published in 1958) can be debated, since it’s not a good match for other bullets designs, but the more streamlined, “VLD” types. it’s nevertheless a good case in point.

Whereas it’s clear that the G7 drag function matches more closely the usual low-drag designs used in long range shooting/hunting than the G1 (something that’s expressed in my website since its beginning) <span style="font-style: italic"> I fall short to notice why Mr. Litz says that the velocity-dependence of G1 is a “problem”, when the same dependence is there with G7 or any other “G” function, because that’s simply unavoidable.</span>

In my estimation that’s perplexing, since that’s the very reason for having a number of “G” functions and not an argument in itself when debating the merits of G7 as a better function to match the current designs, something that was clear for the last fifty years.

<span style="font-style: italic">Both G1 and G7 will respond in the same manner, yielding the same amount of error in drop predictions, given the same variation of, for example, muzzle velocity. And as expected, both will show the same “resilience” to uncertainty in their determination. </span>

No doubt that the work done by the author to flight-test over 170 bullets, is by any standard, a fantastic gift. It’s worth mentioning that along the BC values (G1 and G7) the most critical figure of Cd (Coefficient of Drag) is also published. </div></div>


Basically as I said, I am bi curious, and talk to a host of people and like to explore as many sides of the triangle as possible. I understand it's not always as cut and dry as simply saying, "A" is better, "B" is not. So with that, I genuinely seek out as much detail as possible from all corners of the globe. I try to talk to as many people on any given subject as I can. All for the better understanding of the situation. Being in the shooting industry I tried to be armed with as much details as possible and I like to pass along what I have learned.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">It’s significant to realize, in order to dissipate any confusion that the method used to compute a trajectory based on a G7 value is the same as the one with a G1 value. Just different drag models. Then make your selection to run Siacci/Mayevski, PM, MPM, etc.

Try out making a run using a G7 BC and the output will come close (sub-MOA up to 1500 yards) to another run made by using a well-defined G1 BC (as studied by McCoy, Weinacht, Cooper, Newill). An interested reader can verify that by relying on the data supplied by the book and the accompanying software (which is not a Siacci-based model, thus requiring a near-constant BC along the entire range).

Moreover, every method out there requires the knowledge of a velocity loss descriptor, there is no other way. In that regards, the Pejsa’s method does not impose any extra complexity. In short, if you have velocity data then the coefficients are already in there.

Given the foregoing, I still fail to understand why the Pejsa method is regarded in relation to the bullet’s coefficients as “…which the shooter is burdened to establish…” in particular when Mr. Litz recognizes (rightly so) that “…the accurate determination of a bullet’s BC is not an easy task…” Then my point is, without the flight-data compiled by ballistics labs or individuals, we are going to be lost exactly the same way, with whichever method you like the most.
</div></div>

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: KYpatriot</div><div class="ubbcode-body">Country try Shooter...it is not much money and you can create and save ammo characteristics. </div></div>
Ok Thanks I will look into that also.

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: longdistance</div><div class="ubbcode-body">ya, I found that out today on the stepped bc's today. I didnt think about changing the info on the manufacture bullets. But ya they dont have the stepped numbers for the other brands, such as berger. I called and talked to a guy from sierra about it. It was kinda funny when I was asking him about G7 and entering in a custom burger bullet. But I did do some compairing with it. If i leave the BC at .768 and FPS at 2756 for the 300 SMK it only varies around 4inches off at 1800yards between doing it that way and using the step down. and that is 1-5 BC .768, .760, .750, .750, 750 and velocity ranges 1-4 muzzle to 2300, 2300 to 1800, and 1800 below. So anyway I guess if im going to try out the G7 to compair to G1 for my self I need to get a program that works good with G7. Do you know a good one that doesnt cost a lot.

And I didnt know it was going to get this indepth with this topic. For me I just want to get in the ball park at 1500 to 2200 yards. And then half the fun and good shooting experiance comes from correcting your shot from 1st to 2nd shot. For me, I dont have the money to buy a range finder to figure out a real life scenario target distance that exact to be that exact with a program anyway. And if im at a range weather its at my house or at raton I will then know the distance for sure and can use a programe though, then it would be very good for a 1st round hit for scoring reasions in competition.

Hey <span style="font-style: italic"><span style="text-decoration: underline">Brian</span></span>,

Can you give us the step down G1 BC's of the 338, 300 berger and its velocety boundries for those G1 BC's so that I can use it better in my programe that I have. I promis I will get a programe for G7 and use it also.lol

And dont worry, I will always keep buying Berger Bullets.

When is berger going to make a VLD hunting bullet in .338, 300gr HPBT? You know, for a nice mile long shot on a black bear or elk and have a nice mushroom expansion.

Dont take me the wrong way though, I think it is awsome to be able to punch in some #'s and pull triger and make a first round hit. I learned a lot about ballistics and ballistic programs from this topic. And on the few post of hy jacking the topic, I did not feel that anyone got off topic at all. <span style="text-decoration: underline">A good debate always makes for a better outcome.</span>
</div></div>

Sorry mate I honestly could not recommend a certain program because I have not found one myself yet that suits my purpose.
I use JBM's PMP to model the BC's of my bullets but want to enter that BC data into a handheld device. That is why I purchased JBM ballistic FTE as I thought it would gel with JBM's program. However I spoke with James Brad Millard who is a super generous guy and has been a huge help to me and he says he has nothing to do with the Apple application at all. So I am left confused as to why they say it has the famous JBM ballistic engine? Hey but that is the whole rocket science game they want you to be as confused as possible so they always have a job . I mean look at this debate did anyone get any useful info from Brian or Lowlite I am sure I never did.
I have emailed Brian several times and never ever got a reply but JBM has always been ready to assist where he can .
So based on that I would use the JBM site and his ballistic solvers and play around with the drag functions.

 

[BoilerUP]

Re: Ballistic coefficient G1 and G7

Question:

I notice the baro pressure in LL's examples is listed as 24.92" Hg, but the altitude function is at 0' ASL.

Standard sea-level atmosphere for us aviation types is 29.92" Hg.

I presume the 5" delta in pressure is due to being roughly 5000' ASL?

 

[Mister Ouchie]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: BoilerUP</div><div class="ubbcode-body">Question:

I notice the baro pressure in LL's examples is listed as 24.92" Hg, but the altitude function is at 0' ASL.

Standard sea-level atmosphere for us aviation types is 29.92" Hg.

I presume the 5" delta in pressure is due to being roughly 5000' ASL?</div></div>

Makes sense, the actual altitude shouldn't matter as long as you have the absolute pressure.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Pressure is Absolute and my range is at 5300ft above sea level, so the altitude is not used.

Note it says, "Pressure not corrected" if it were I would then be required to use the actual altitude

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

There are several things I'd like to respond to over the last several posts.

1) The algorithm, vs the model, vs the drag curve.
Ballistic solvers are comprised of two basic parts:

A) The '<span style="font-weight: bold">algorithm</span>', aka the simulation. This is the basic framework for solving the equations of motion. These equations of motion are not debatable, arguable or questioned since Newton established them. In particular, it's newton's second law (F=ma) which equates force to an objects mass and acceleration. In ballistics, the force is aerodynamic drag, the mass is the bullet, and the acceleration (or de-celeration) is the bullet slowing down. The acceleration is integrated to get velocity, which is integrated to get position, and the trajectory is solved. This is just how it's done. It's the same equations of motion that every modern fire control is based on. Needless to say, some amateur programs fail to properly code the equations of motion, or use approximations that compromise the calculations in some way. The Pejsa approach is an example of an approximation. It was much more handy to use approximations before modern computers were able to solve the equations directly (numerically)

B) the <span style="font-weight: bold">model</span>. There is an atmosphere model that has to calculate the correct air density based on temp, pres, hum. This is one task that several amateur programs fail to do correctly, or will mix elements of the ASM and ICAO atmospheres, or not match the atmosphere model to the atmosphere used to calculate a BC. Anyway, the atmosphere is one model in the ballistic 'simulation'.
Another model, the one which is the topic of this thread, is the bullet model. The diameter and mass of the bullet are two important but easy elements to model. The drag coefficient of the bullet as a function of speed is the difficult one to model. For several reasons it's convenient to reference a bullets drag to a fitting standard. G1 and G7 are two of the many options for standard drag models.

The standard most representative of long range bullets is the G7.

When G7 BC's are measured and corrected for a standard atmosphere model, and that same atmosphere model is used in a properly written ballistic solver (algorithm), there will be very little error in the predicted trajectories.
The large caveat here is that all the inputs have to be accurate. It doesn't matter if you're using all the right tools, BC's, atmosphere model, etc, if you're MV is 50 fps faster or slower than you think and input, the predictions will likewise be off. If you enter the same set of inputs into a poorly written, uncoordinated program, it may actually appear to be closer to the observed drop because the errors in the program can offset the 50 fps error in MV (this speaks to what Cory and KY agreed to).

The point is that there is a 'right' way to model the equations of motion (algorithm). The algorithm itself doesn't require alteration. There are no crazy genius out there who can improve on the equations of aeroballistic motion (Newton was the crazy genius). Likewise the atmosphere is well understood and if written properly, a program can assign the appropriate air density to a given set of temp/pres/hum. There is room for improvement in modeling bullets, as even the G7 model isn't perfect for every bullet. Although it is 'good enough' to get you within 1 click thru the supersonic range of the trajectory (2 experimental examples of this in chapter 8). 'Custom drag curves' for bullets that don't rely on referencing a standard offer improvement over G7 referenced BC's. However getting them is a challenge and the improvement is trivial for supersonic ranges.

The benefits of the standard way of doing things as described above is that BC's can be measured and stated for all to use. If the BC's are plugged into properly written solvers, they will produce the same results, for everyone, all the time, everywhere. Then why, you may ask, don't all programs give the same results? The answer to that question is that not all solvers are properly written! Is is really a suprise that that $2.99 app you bought or that 30 yr old software package may not be perfect? JBM, and anything running my solvers produce the same results BECAUSE they're both properly written. Anything that doesn't match them is in error by the amount they differ. If you 'hit closer' with something else, it's because there are other errors in the system which offset the error of the solver.

LB. As I stated in a previous post, LB is a one off. The fact that it produces the same solutions with G7 and G1 is direct evidence that it's not modeling G1 and G7 the way they actually are. The two trajectories SHOULD be different because they're different drag models. I hate to be against LB because I know Gus and consider him a friend. But the fact is that his system is simply not compatible with modern ballistics. Example. I've published a book with hundreds of BC's for modern bullets that will work well for any standard solver. Where's the book of 'LB' BCs that work just with that program? Until there is such a source of matched data for that solver, users have to find their own BC's that work with that unique program. Some users don't mind that and it's fine. However my objective is to provide predictive capabilities to the masses. Having 'one off' programs out there and people advocating them confuses the issue for shooters who are trying to learn the conventional approach.

Enough on solvers for now.

2) LL. "I didn't hear about G7 in sniper school in the '80s, so why do we need it now?" C'mon man, really? At some point fuel injection was new too. You're basically advocating a mindset that isn't open to change. When there's a better way of doing things, if you don't want to advance, that's fine. But there's no reason to hold everyone back with you.
You say you talk to 'many experts' about ballistics. The only material you've referenced in this thread; LB and those quotes come from the same guy (Gus). And that's a guy who's selling his own special brand of software. Critical thinking.

3) LL (again). You said you don't use my .243 G7 for the 175 SMK in your new gun the same as all the rest, but that you use .239 instead. To put that in perspective, that's an error of 1.6%. 5" at 1000 yards. And that's assuming everything else is right. What your saying is that you can pick up a new rifle as if you've never shot 175 SMK's before. Used my .243 G7, and been within 5" at 1000 yards (of course after getting all the other inputs right). I find that an acceptable result. You've also described in another thread (a while ago) how all the programs gave different results and that some needed a G7 quite different than .243 to match your data. But in a program that used a standard solver (I forget if it was JBM or one of mine) .243 was right on. That's what I'm talking about regarding the value of standardized methods. That's how they should work. Throw other variations into the mix and it's easy to be confused, but if you stick with the conventional solvers and matched standard data, the results are very good (caveat once again; assuming everything else is right).

It's an important caveat because if you don't get everything else right, then you can't attribute a hit or a miss to G1 vs G7 at all.

Some other facts that make the G1 paradigm difficult to deal with.
<span style="font-weight: bold">Stepped BC's.</span> You can improve the effectiveness of G1 BC's by stepping them. But why go thru this complication if it's not necessary?
<span style="font-weight: bold">Velocity dependence.</span> Bullet company 'X' might test and advertise a perfectly accurate G1 BC over 100 or 300 yards. But that BC, despite being technically 'accurate' will not be effectively accurate for a 1000 yard trajectory. Furthermore, the BC that's right for 1000 won't be right for 1500, etc. G7's have this same problem, but it's much much less, and for practical purposes you can ignore it's effects because it's less than a click.
<span style="font-weight: bold">Methods for determining G1 BC.</span> If you measure a G1 BC based on tof vs one based on velocity decay, you'll get <span style="font-style: italic">two different numbers!</span>. The reason again goes back to the mismatched drag curve.

Considering all of the above, the only reason I can every see why someone would choose G1 over G7 for a modern long range bullet is if there simply isn't a G7 BC available. Even then, if you're going to have to 'tweak in' a G1 because the one supplied is probably not accurate to begin with, then why not 'tweak in' a G7 BC? It will be more extensible in other situations and velocities than the G1.

I hope I don't offend LL enough that he takes his pixels and goes home. I suspect there are many who are learning from this thread.

-Bryan

 

[TiroFijo]

Re: Ballistic coefficient G1 and G7

Bryan, I agree to use the curve that fits best, but just looking at the nice outlines of the standard bullets is a bit misleading...

I think you also have to take into account the diameter of the test bullet that originated the drag model.

The "american" (Ingalls) G1 standard bullet is 1" in diameter (surely the original german and french were other diameter?), and this is the reason why comparing it with other very different (more aerodynamic) bullet shapes, but with smaller diameters, still does a pretty decent job. Sierra claims that in their tests the G1 curve fits best for most of their bullets, boat tail or not, and they tested at different velocities, much more than other makers (until perhaps 10 years ago or so). Perhaps not valid for their long range bullets, but OTOH their "stepped" BCs for their bullets in current military use (.224" 77 SMK; and .308" 175, 190 and 220 SMK) are based on true doppler radar and chrono data on Aberdeen PGs. This is as good as it gets, and IMO beats the theoretical better fit of a certain drag curve.

Same for radar data on the Lapua bullets, WAY better than arguing "my drag curve is better than yours". This radar data (and fitting whatever program you have to get the proper results) should really be the new standard, not semiobsolete BC notions. Even "real world" personal data is sometimes dubious at long range due to difficult to measure external factors.

Everytime you deviate from the base bullet (in shape OR diameter) your BC is not going to be identical. If the shape and diameter deviations are small, then the curve fits best.

What is the diameter of the test G5 and G7 standard bullets?

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">Bryan, I agree to use the curve that fits best, but just looking at the nice outlines of the standard bullets is a bit misleading...

I think you also have to take into account the diameter of the test bullet that originated the drag model.</div></div>

Actually, the diameter and mass are irrelevant to the drag curve. It doesn't matter if the standard projectile is 1", .30 cal, 20mm, etc. Mass and cross section are accounted for separate from the non-dimensional drag curve.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The "american" (Ingalls) G1 standard bullet is 1" in diameter (surely the original german and french were other diameter?), and this is the reason why comparing it with other very different (more aerodynamic) bullet shapes, but with smaller diameters, still does a pretty decent job. </div></div>

I disagree completely.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Sierra claims that in their tests the G1 curve fits best for most of their bullets, boat tail or not, and they tested at different velocities, much more than other makers (until perhaps 10 years ago or so). </div></div>

If G1 was a good fit, they wouldn't need to piece-wise define it by velocity. G7 does still have velocity variance, but much much less than G1 for modern BT bullets. Having 3% difference in BC from muzzle to target is better than having 20% difference.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Perhaps not valid for their long range bullets, but OTOH their "stepped" BCs for their bullets in current military use (.224" 77 SMK; and .308" 175, 190 and 220 SMK) are based on true doppler radar and chrono data on Aberdeen PGs. This is as good as it gets, and IMO beats the theoretical better fit of a certain drag curve.</div></div>

I agree that they're stepped G1 BC's for those bullets are not bad. However a single G7 BC is more convenient, and less error prone.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Same for radar data on the Lapua bullets, WAY better than arguing "my drag curve is better than yours". This radar data (and fitting whatever program you have to get the proper results) should really be the new standard, not semiobsolete BC notions. </div></div>

Note that Lapua, within a year of having radar test data available for many of their bullets, chose to publish G7 BC's for their bullets.
I agree that custom drag curves have a place in the future of consumer level ballistic modeling. But there are too many conveniences of BC's to do away with them. For example, the ability to quickly compare bullet performance can be done by comparing BC's. This convenient summary of performance isn't possible when using custom drag curves.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Even "real world" personal data is sometimes dubious at long range due to difficult to measure external factors.

Everytime you deviate from the base bullet (in shape OR diameter) your BC is not going to be identical. If the shape and diameter deviations are small, then the curve fits best.

What is the diameter of the test G5 and G7 standard bullets? </div></div>

As stated above, diameter and mass are not relevant to a drag standard. That's simply how coefficients work.

-Bryan

 

[goober]

Re: Ballistic coefficient G1 and G7

Beat thread on the Hide , great explanation Bryan !

 

[TiroFijo]

Re: Ballistic coefficient G1 and G7

"Actually, the diameter and mass are irrelevant to the drag curve. It doesn't matter if the standard projectile is 1", .30 cal, 20mm, etc. Mass and cross section are accounted for separate from the non-dimensional drag curve."

I disagree... while sectional density can be easily calculated, the form factor (and thus BC) cannot. You need firing tests to establish it accurately, and the larger the shape of diameter variation the more difficult it is to estimate it accurately.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Bryan,

I have no interest in taking my pixels and going home and again, I acknowledge what a great job you do and what you have done for the shooting community. No questioning the influence and the contribution, so I see no reason to be angry at all. You have your opinion, myself and others have ours and the reader can decide which way the water flows.

Unlike most, I was actually at the range shooting, AGAIN, just like you said, I tend to live in the real world, which one could say fills my logbook with actual data. I like to test theory against reality and if it is not working across the board universally, I have to conclude there is a hidden motive, or meaning to it.

However I will say, I never wrote what you quoted as being attributed to me ? Didn't use G7 in sniper school ? I said that ? If so I can't find it ? I can honestly say in 1986 I had no idea what the BC of the bullet was, (173gr) it was irrelevant for me. All my data from shooting and I really didn't even know what the drop was for my M40A1, other than, 8 -2 (800yards) or 5+1, (500 yards) still graduating Sniper school was quite the accomplishment for a young PFC.

I did note that according to Gus, G7 had been around since 1958 and was largely ignored by the establishment, until the last few years. That I acknowledge saying. I will not tell you what "others' have said, Like Gerald Perry when this discussion was had, it was not polite and repeating it would be bad form. Seriously. I have also spoke to someone else, who's name I won't mention, again, bad form, fortunately Gus will go on the record. Hence the use of his quotes. But let me say no less than 3 people where spoken too.

Also, since we are quoting, here are some BLITZ quotes regarding Pesja and LB:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">You make some good valid points about the Pejsa approach. No doubt you know it well, as that's what your program uses as a solution engine. I would be interested in a discussion on the merits of the various approaches (Pejsa/Siacci/PM, etc) on another thread, but I'd rather avoid having it here.

Great work on Loadbase by the way! Your feature set is second to none, and you're the first one to offer a G7 capability in a (non-iPhone) mobile device. You're to be commended for listening to your users and providing them with the useful options they want/need to be more successful shooters. </div></div>

That was you... as was this

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> On the Point Mass method…

“…Now if you had good representations of your CD function in the closed form method, you won’t gain much (if any) accuracy with a POINT MASS model, but you will experience significant increases in computer run time…”

cannot be clearer the foregoing statement…isn’t it?

If I were to write a ballistics program for small arms that’s intended to surpass the existing available packages, I would base it on Pejsa’s method for the following reasons:

· The analytic solution method is fast, which is a requirement for field use (Siacci also has this feature).
· The program does not require you to store large tables (S, T and V functions) like the Siacci method.
· You can make use of advertised BC’s (Siacci also has this feature).
· If you care to go to the trouble of test firing a specific projectile, you have the potential to customize the drag function for that one projectile. This cannot be done as easily or as accurately with the Siacci method.

Basically, point #5 is the only improvement my code would have over Pejsa’s currently available package.

As an aside, I work for the Air Force as an Aerospace Engineer. I wrote a fire control program for air-to-air missile engagement zones based on a combination of Pejsa’s method, and McCoy’s flat fire equations (Chapter 5 of Modern Exterior Ballistics).</div></div>

Also haven't' you been recently advocating Banding or Stepping G7 ? I seem to recall you mentioning this. And because JBM automatically steps G1, there is absolutely no extra work at all... it's automatically done for me?

The point of saying I have tweaked G7 is simply to demonstrate it takes the same amount of work. If i have tweaking G1 (which you shouldn't have too, there is too much data available) and G7, even a few points, its the same amount of work.

No matter what, I am gonna calibrate and adjust my software to match my real world data. So if I am gonna do it for one I am gonna do it for both. Like CoryT said, it's really a wash in the real world. And for most it is just as easy to use G1 as it is G7 with one very big caveat. G1 data is everywhere for pretty much everything and G7 is not. A person can't adjust what he doesn't have access too.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">... You need firing tests to establish it accurately, and <span style="text-decoration: underline">the larger the shape of diameter variation the more difficult it is to estimate it accurately</span>.
</div></div>

I don't follow the underlined statement.

BC = SD/i
where:
SD = Sectional Density (weight/diameter^2)
i = form factor

The SD 'part' of BC accounts for the mass and diameter of the projectile. The form factor addresses the <span style="font-style: italic">non-dimensional</span> drag coefficient.

To elaborate on form factor, this is the drag coefficient (Cd) of a bullet divided by the Cd of a standard bullet, at a given Mach number. So for example, the drag coefficient of the G7 standard at Mach 2.5 (2790 fps in standard conditions) is 0.270. If the drag of your bullet at this Mach number is 0.280, then the form factor is .28/.27 = 1.037. In other words, the drag of your bullet is 3.7% greater than the G7 standard. This calculation is independent of the mass and diameter of the bullet.

It might help to lay out the fundamental calculation of aerodynamic force on a bullet. Starting with Newtons second law:

F = ma
where:
F = force (in lb)
m = mass (of the bullet, in sl)
a = acceleration of the bullet (in ft/s^2)

Typically this equation is solved for a:
a = F/m

The mass of the bullet is easy. For this example, we'll use the .30 cal 175 SMK.
m = weight in grains/7000/32.2
m = 175/7000/32.2 = 0.000776 sl

Now on to the interesting part, the force (F). This is the aerodynamic force, in lb, that the air exerts on the bullet. This force is calculated by the equation:
F = 1/2*p*V^2*Cd*S
where:
p = air density in sl/ft^3
V = velocity in fps
Cd = drag coefficient (non-dimensional)
S = cross sectional area of the bullet in sq feet (this is what Cd is non-dimensionalized by, which is why caliber doesn't matter with drag curves)

So we'll use standard air density: 0.002377 sl/ft^3
Velocity of 2790 fps
Cd of 0.293 (the 175 SMK has a G7 form factor of 1.085, which means it's Cd at Mach 2.5 is .27*1.085 = .293)
S = pi*r^2 = pi*(.308/2/12)^2 = .000517 ft^2

So the force on the bullet is:
F = 1/2*.002377*2790^2*.293*.000517
F = 1.40 lb.

Going back to Newtons second law and solving for acceleration, we get:

a = F/m
a = 1.40/0.000776
a = 1842 ft/s^2

In other words: 1842/32.2 = 57 G's.

So at the moment when the bullet is traveling 2790 fps, it's acceleration is -1842 feet per second per second.

Wanna check the math?

Running a <span style="font-style: italic">standard</span> ballistics solver, enter a MV of 2790 fps for the 175 SMK in standard conditions and see how much time it takes the bullet to go 10 yards. My program says 0.0108 seconds. Now if the acceleration we calculated above is accurate, the bullet should slow down:
-1842 fps per second, or
-1842*0.0108 = -19.9 fps in the 10 yards.
That would be: 2790 - 19.9 = 2770.1 fps.
Indeed the program says the velocity is 2771 fps in 10 yards. The reason for the .9 fps difference is
a) as the bullet slows from 2790 fps to 2789, 2788, etc, the deceleration likewise decreases, so it doesn't loose the full 19.9 fps.
b) rounding error.

In an actual program, time steps of 0.001 seconds or smaller are taken to reduce a and b to negligible amounts. The velocities are computed at each step, and the positions follow by integration.

So there is is, derivation of the aero ballistic equations of motion (at least the parts relavent to this discussion).

Clearly the drag curve, being non-dimensional, is not affected by the caliber or mass of the standard projectiles, but only by it's shape.

-Bryan

 

[ctressler]

Re: Ballistic coefficient G1 and G7

It might be just the engineer in me talking, but that is a beautiful post Brian.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">Bryan,

I have no interest in taking my pixels and going home and again, I acknowledge what a great job you do and what you have done for the shooting community. No questioning the influence and the contribution, so I see no reason to be angry at all. You have your opinion, myself and others have ours and the reader can decide which way the water flows.

Unlike most, I was actually at the range shooting, AGAIN, just like you said, I tend to live in the real world, which one could say fills my logbook with actual data. I like to test theory against reality and if it is not working across the board universally, I have to conclude there is a hidden motive, or meaning to it.

However I will say, I never wrote what you quoted as being attributed to me ? Didn't use G7 in sniper school ? I said that ? If so I can't find it ? I can honestly say in 1986 I had no idea what the BC of the bullet was, (173gr) it was irrelevant for me. All my data from shooting and I really didn't even know what the drop was for my M40A1, other than, 8 -2 (800yards) or 5+1, (500 yards) still graduating Sniper school was quite the accomplishment for a young PFC.

I did note that according to Gus, G7 had been around since 1958 and was largely ignored by the establishment, until the last few years. That I acknowledge saying. I will not tell you what "others' have said, Like Gerald Perry when this discussion was had, it was not polite and repeating it would be bad form. Seriously. I have also spoke to someone else, who's name I won't mention, again, bad form, fortunately Gus will go on the record. Hence the use of his quotes. But let me know no less than 3 people where spoken too.

Also, since we are quoting, here are some BLITZ quotes regarding Pesja and LB:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">You make some good valid points about the Pejsa approach. No doubt you know it well, as that's what your program uses as a solution engine. I would be interested in a discussion on the merits of the various approaches (Pejsa/Siacci/PM, etc) on another thread, but I'd rather avoid having it here.

Great work on Loadbase by the way! Your feature set is second to none, and you're the first one to offer a G7 capability in a (non-iPhone) mobile device. You're to be commended for listening to your users and providing them with the useful options they want/need to be more successful shooters. </div></div>

That was you... as was this

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> On the Point Mass method…

“…Now if you had good representations of your CD function in the closed form method, you won’t gain much (if any) accuracy with a POINT MASS model, but you will experience significant increases in computer run time…”

cannot be clearer the foregoing statement…isn’t it?

If I were to write a ballistics program for small arms that’s intended to surpass the existing available packages, I would base it on Pejsa’s method for the following reasons:

· The analytic solution method is fast, which is a requirement for field use (Siacci also has this feature).
· The program does not require you to store large tables (S, T and V functions) like the Siacci method.
· You can make use of advertised BC’s (Siacci also has this feature).
· If you care to go to the trouble of test firing a specific projectile, you have the potential to customize the drag function for that one projectile. This cannot be done as easily or as accurately with the Siacci method.

Basically, point #5 is the only improvement my code would have over Pejsa’s currently available package.

As an aside, I work for the Air Force as an Aerospace Engineer. I wrote a fire control program for air-to-air missile engagement zones based on a combination of Pejsa’s method, and McCoy’s flat fire equations (Chapter 5 of Modern Exterior Ballistics).</div></div>

Also haven't' you been recently advocating Banding or Stepping G7 ? I seem to recall you mentioning this. And because JBM automatically steps G1, there is absolutely no extra work at all... it's automatically done for me?

The point of saying I have tweaked G7 is simply to demonstrate it takes the same amount of work. If i have tweaking G1 (which you shouldn't have too, there is too much data available) and G7, even a few points, its the same amount of work.

No matter what, I am gonna calibrate and adjust my software to match my real world data. So if I am gonna do it for one I am gonna do it for both. Like CoryT said, it's really a wash in the real world. And for most it is just as easy to use G1 as it is G7 with one very big caveat. G1 data is everywhere for pretty much everything and G7 is not. A person can't adjust what he doesn't have access too.
</div></div>

My apologies if I misquoted your exact words. The implication of the statement was clear, at least to me.

As to my quotes, there was a time many years ago before I'd written any ballstics programs when I did publish and believe that quoted material. If you've visited that same article in the past several years, you'll see the relavent parts have been replaced to read:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If I were to write a ballistics program for small arms that’s intended to surpass the existing available packages, I would use a point mass solver (3-DOF numeric solver) for the following reasons:
1. Modern computers, even field deployable devices like palm pilots and cell phones have fast enough processors these days to solve a numerical solution in a reasonable amount of run time.
2. The program does not require you to store large tables (S, T and V functions) like the Siacci method.
3. You can make use of multiple standards (G1, G7, etc) depending on whichever one is best suited to the bullet you’re modeling. (Siacci also has this feature).
4. If you have access to a 6-DOF simulation, you can investigate trends like gyroscopic drift as a function of flight time for certain classes of projectiles, and then apply the trends as corrections to the point mass solution (Ref article: Extending Max Effective Range of Small Arms on this website). Applying the 6-DOF corrections won’t significantly affect computer run time.

I would avoid the Pejsa solution because of the difficulty of modeling bullet drag. Since the Pejsa method does not make use of any standard projectile drag curves, it’s up to the user to describe the drag of his own bullets. This requires establishing obscure coefficients and exponents for each bullet for several velocity bands. Large compromises are made when the projectile slows to transonic speeds and the drag curve is approximated with linear segments. The complexity of Mach dependant projectile drag belongs in the solution method, it should not be up to the shooter to figure out.</div></div>

I was initially impressed with the Pejsa approach, and did use a version of those equations in a specialized program that was written specifically to run in an environment with very limited processing resources. Under those circumstances, approximate equations are the only way to get an answer sometimes. Also if you're modeling missiles which aren't conventionally modeled with BC's, there's no standardization issues.

When dealing in the current modern world with capable processors and standardized BC's, approximate approaches like Pejsa's are simply unnecessary compromises.
In fact, back when I did the MOBALL device; that dog of a processor wouldn't run the full equations in a timely manner, so I resorted back to approximate methods, but they were modeled around G1 and G7 standards, that worked well with (matched) properly written programs; not tweaked one offs. Fortunately I've since teamed up with a programmer who's very competent at programming for more relevant (android, iOS) platforms, and has brought my solver to those more capable platforms.

I likewise have respect for your (Frank) knowledge and experience which is broad. My expertise is focused on ballistics and Palma shooting. However in those areas I'm rather well versed and confident. Our relative strengths will probably not escape the readers as they weigh our ideas on this subject.

-Bryan

 

[TiroFijo]

Re: Ballistic coefficient G1 and G7

Bryan:

"Clearly the drag curve, being non-dimensional, is not affected by the caliber or mass of the standard projectiles, but only by it's shape."

So, are you saying that you can take a .17" caliber bullet and a 1.0" one, both with the same shape and proportions (say, both fit the G7 profile), and (knowing the weight of course) you can <span style="font-weight: bold">accurately</span> calculate the BC just scaling to the G7 curve

?

 

[JL]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Bryan Litz</div><div class="ubbcode-body">

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Same for radar data on the Lapua bullets, WAY better than arguing "my drag curve is better than yours". This radar data (and fitting whatever program you have to get the proper results) should really be the new standard, not semiobsolete BC notions. </div></div>

Note that Lapua, within a year of having radar test data available for many of their bullets, chose to publish G7 BC's for their bullets.
I agree that custom drag curves have a place in the future of consumer level ballistic modeling. But there are too many conveniences of BC's to do away with them. For example, the ability to quickly compare bullet performance can be done by comparing BC's. This convenient summary of performance isn't possible when using custom drag curves.
-Bryan </div></div>
Lapua published G7 data (too) for their bullets simply because certain market areas are keen to use it. It is unclear to me why, as I also do not understand why Chevy still uses pushrods in their motors.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: TiroFijo</div><div class="ubbcode-body">Bryan:

"Clearly the drag curve, being non-dimensional, is not affected by the caliber or mass of the standard projectiles, but only by it's shape."

So, are you saying that you can take a .17" caliber bullet and a 1.0" one, both with the same shape and proportions (say, both fit the G7 profile), and (knowing the weight of course) you can <span style="font-weight: bold">accurately</span> calculate the BC just scaling to the G7 curve

? </div></div>

Of course. That's the entire reason for having dimensionless coefficients.

If the bullet has a G7 form factor of 1.0 (for example, this would mean it's shape is the same as the G7 standard), then it's G7 BC would be equal to its sectional density.

If the .17 caliber bullet weighs 40 grains, it's SD and G7 BC would be .137.

If the 1" bullet weighed 7213 grains (1.03 lb, which is the 40 grain .17 cal scaled up in all dimensions) it's SD and G7 BC would be 1.03.

All aerodynamic (force) coefficients work this way. The coefficients that deal with moments (torque) also include an additional length term in the equation (caliber) which non-dimensionalizes the moment coefficient, quantifies the moment arm, and allows for the rotational force to be calculated. This becomes relevant in stability calculations.

I didn't think this sh!t up. But those who did knew what they were doing. I just learned about it in aerospace 101.

-Bryan

 

[TiroFijo]

Re: Ballistic coefficient G1 and G7

Bryan, I know you did not made this up, and know how to theoretically calculate BCs for each caliber, etc. Just don't buy it, for <span style="font-weight: bold">accurate</span> calculations

what about the airflow dynamics? Are they the same for a .17" or 1.0" bullet?

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

I want to go in a similar direction but with a different real world representation...

Using the recent 338LM bullet test we did at Gunsite, I want to demonstrate an example of my "leeriness" towards modeled data.

Let's take the GS Custom bullet arguments, specifically the 295gr SP.

GS of GS Custom argued on here for months about his numbers, and his profile for the 295gr 338 bullet. It was marketed and sold to people all over the world, and in fact you can right now go to JBM and pull it from their library. <span style="font-style: italic">(I will show this in a second)</span>

it was talked about in highly technical terms, the flight characteristics, the history of the design, the modeling done to prove it was successful. I even got a few nasty emails from GS himself telling me about the data from the Horus ATRAG Software that gave it great numbers out to distance. How we didn't have to do anything because the Horus software said...

Fast forward to real life, and three different people with 3 different rifles, all accomplished ELR shooters, and reloaders take this bullet out and voila it will not fly past 700 yards. For any of us.

At Gunsite we tried to hit at car at 1000 yards with this bullet and were unable to get it to fly. There was talk of new versions, old versions, too much velocity, not enough velocity, a whole range of excuses.

Yet before anyone shot it, the techno-babble was hard and heavy, which says,

This bullet has a BC of 1.010 G1... real life problem is, it doesn't fly.

So, when we debate G1 vs G7 and the real world data points to an equal amount of success, with an equal amount of fine tuning / calibrating, you have to look at that actual data, at least in my opinion.

I completely get it, the books say, G1 should not work for a boat tail bullet as well as G7, however the reality on the ground tells a long and different tale. So the question can be, "why", or "yes but it is an accident of circumstance" or "well it shouldn't / can't" ---> still here we are and it does.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">LB. As I stated in a previous post, LB is a one off. The fact that it produces the same solutions with G7 and G1 is direct evidence that it's not modeling G1 and G7 the way they actually are. The two trajectories SHOULD be different because they're different drag models. I hate to be against LB because I know Gus and consider him a friend. But the fact is that his system is simply not compatible with modern ballistics. Example. I've published a book with hundreds of BC's for modern bullets that will work well for any standard solver. Where's the book of 'LB' BCs that work just with that program? Until there is such a source of matched data for that solver, users have to find their own BC's that work with that unique program. Some users don't mind that and it's fine. However my objective is to provide predictive capabilities to the masses. Having 'one off' programs out there and people advocating them confuses the issue for shooters who are trying to learn the conventional approach</div></div>

Field Firing Solutions uses the same DK factor, and has a similar output as Patagonia Loadbase / ColdBore. Because they work as well as they do with both G1, I don't' see how you can debate it as being a "problem". One off or otherwise, especially if they are based on a known model like Pesja. These programs are using the standard BC numbers and are not changing them. I put in the commonly used data and they both give me solid results, and I have shot them religiously out to 2000m. Gunsite lives by FFS, which is also a Pesja based system. So that cannot be described as a 1 off program, at least not in my opinion.

I get what the premise is, I just don't understand how reality can differ so far from academia on this subject. Which is why I tend to question things like I do. When the science of the shot says, "The answer must be X" and I go and shoot it and the answer is "Y", over and over and over again, coming at it from 3 different directions trying to get a consistent "X" answer, you begin to take notice when it is routinely "Y".

here is the JBM data, right from the library.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

TiroFijo,

Until you shrink to a scale that is on the order of air molecules (much smaller than .17 caliber), the coefficient approach is valid.

Frank,

I don't know GS personally. But I've measured dramatically different BC's for his bullets than what he advertises (this was common for most monolithic bullets I tested). What that tells me is that he is not <span style="font-style: italic">properly</span> representing the performance of his bullets. Basically this is the same conclusion you came to.

That brings up a credibility issue with theory. Just because the 'theoretical' results with bullet X, from person X didn't pan out shouldn't discredit any theory you ever hear. Some people have a better grasp of theory than others and their predictions can be regarded as more reliable.

Regarding the GS issue, 'theory' suggests a possibility in which you're both right. If GS's testing was done at a substantially higher altitude (or DA) than yours, it could be that his observations and reports are entirely factual due to the bullet remaining stable in that atmospheric environment. If you tested in a lower altitude environment than him, that could account for the lack of stability and poor results. It's quite common for shooters to argue about what twist it takes to stabilize a given bullet and many times it's because their observations are from different altitudes and they're both right.

But back to the point, you probably wouldn't dismiss NASA's ability to successfully launch a shuttle (in 2012) because you saw a neighbor kid blow up his model rocket. Likewise, maybe you shouldn't question a professional ballistician on the grounds that a machinist couldn't predict the performance of his bullets accurately.

-Bryan

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

Clearly I am not the only one, as you stated earlier.

My only <span style="font-style: italic">"questioning"</span> was with the idea that G1 was a <span style="text-decoration: underline">problem</span> and only really working by accident. The idea of completely poo, poo'ing it all together.

Also I would like to think my observations are a bit closers to Apples to Apples, maybe I am debating Granny vs Macintosh, but still apples. I don't' think I swing to the Lotto Machine side of things.

Still that machinist was proud to show off computer models, which was my point.

I would tend to think we were actually at a higher altitude, we were shooting at DA around 6000ft at the height of the day. I don't know where he shot them, if at all. But certainly that debate is over.

Still that does bring us back to Pesja and FFS along with LB3... ? If they work so well why argue it. The end results are what matters and in the end, they give solid repeatable results that rival any other programs on the block. If you look at their track record, given a life or death situation with UKD targets out to any distance, I would want one of these over any other piece of software I have used.

I will say, the G7 based FDAC is equally excellent, hence my opinion to use them both, G1 in FFS or LB3, and G7 in anything not those two.

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

We're probably not as far opposed as it may have seemed.

The lotto comment was only used to exaggerate the thought process; an analogy to make a point. Not saying that G1 was 'so bad' you might as well play the lotto. The point of the analogy was to say if the method that you know is less accurate (G1) happens to produce a closer prediction sometimes (among many other error sources), do you conclude that G1 is now better, or that error is at play?

Anyway, G1 based solutions can obviously be useful, once you've found the right G1 for your speed band. Once you 'dial it in', there are many G1 programs that can give you very useful data. But here's my thing; you have to tell the program what you shot (thru tweaking BC), so it can tell you what you will shoot. But with the G7 based solvers and BCs that I advocate, you get closer to true predictions from the very first shot. This played out with your new rifle that you said had to use .239 instead of .243. Some may see that as simply being 'wrong', I see it as 1.6% error that results in 5" error at 1000 yards. Compared to other alternatives, I believe that will get you closer to a first shot hit without tweaking it than other options.

-Bryan

 

[siracusap]

Re: Ballistic coefficient G1 and G7

Bryan,

Had a question for you I've been wanting to ask you for some time and this seems like the right thread. If you look at the G1 and G7 numbers for any of the 90 grain .224 Berger bullets they are clearly superior to the 155.5 .308 or any other 155 made by Sierra et al. However no one shoots them in the FTR category where you are limited to either the .223 or .308. By no one I mean none of the top shooters and no one to my knowledge has ever placed very well with them at the national/world level, consistently at least. The "complaint" with them is that they aren't less inherently accurate than the 155's, but that in heavy wind they get tossed around more even when driven at a comparable FPS. Obviously this isn't a scientific conclusion, purely anecdotal, however I think you would have to agree that is the perception, at least among FTR shooters. Would you agree with that perception and if so, why don't the G1/G7 numbers translate on paper relative to the 155's?

 

[BryanLitz]

Re: Ballistic coefficient G1 and G7

I think the reason why the 90 gr .224's aren't favored is due to their 'finicky-ness', for lack of a better word. It's just such a long bullet, and all that bearing surface in such a small bore, with super fast twist... everything adds up against them being reliable, repeatable performers accuracy wise. I know many people who've messed with them long enough to get them to shoot great groups, for a while. But I don't know of anyone who's successfully campaigned them for an entire season with the reliable success of the .308 with 155/185 grain class bullet.

If I were to shoot a .223 in competition, I would choose a 80 grain class bullet. It's still long, but is back off all the extremes of the 90 grainers.

As to effects in wind, I think it is as good in the wind as the G7 predictions suggest. However the lack of reliable accuracy negates the wind performance.

Sorry to say, but my motto is: "friends don't let friends shoot 90 gr .22 bullets!"

-Bryan

 

[siracusap]

Re: Ballistic coefficient G1 and G7

Thanks for the answer Bryan.

 

[Country]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Savage10FCPK</div><div class="ubbcode-body">Bryan,

Had a question for you I've been wanting to ask you for some time and this seems like the right thread. If you look at the G1 and G7 numbers for any of the 90 grain .224 Berger bullets they are clearly superior to the 155.5 .308 or any other 155 made by Sierra et al. However no one shoots them in the FTR category where you are limited to either the .223 or .308. By no one I mean none of the top shooters and no one to my knowledge has ever placed very well with them at the national/world level, consistently at least. The "complaint" with them is that they aren't less inherently accurate than the 155's, but that in heavy wind they get tossed around more even when driven at a comparable FPS. Obviously this isn't a scientific conclusion, purely anecdotal, however I think you would have to agree that is the perception, at least among FTR shooters. Would you agree with that perception and if so, why don't the G1/G7 numbers translate on paper relative to the 155's? </div></div>

This basicly is what Lowlite is trying to convey . When the theory and predictions don't match the real world !

 

[RemingtonSPS]

Re: Ballistic coefficient G1 and G7

Some of the error we have seen for ballistic coefficients is based on velocity. Most if not all of Brian's BC's are an "average" BC from 3,000fps-1,500fps. If you have a muzzle velocity of 2,800fps the "average" BC is going to be lower than the stated BC (marginally). We have also seen this with Sierra bullets because, even though they give you stepped G1 BC's, their average is based on 2,800fps muzzle velocity or 2,600fps muzzle velocity. We have seen this in particular with the 375 Cheytac round. When you are pushing a muzzle velocity of 3,300fps the "average" BC goes way up.

I'm wondering if a guy shooting an 18" barreled .308 win with the 175 SMK is getting the lower than stated BC because of this.

 

[Lowlight]

Re: Ballistic coefficient G1 and G7

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: MuleHunter</div><div class="ubbcode-body">Some of the error we have seen for ballistic coefficients is based on velocity. Most if not all of Brian's BC's are an "average" BC from 3,000fps-1,500fps. If you have a muzzle velocity of 2,800fps the "average" BC is going to be lower than the stated BC (marginally). We have also seen this with Sierra bullets because, even though they give you stepped G1 BC's, their average is based on 2,800fps muzzle velocity or 2,600fps muzzle velocity. We have seen this in particular with the 375 Cheytac round. When you are pushing a muzzle velocity of 3,300fps the "average" BC goes way up.

I'm wondering if a guy shooting an 18" barreled .308 win with the 175 SMK is getting the lower than stated BC because of this.</div></div>

Tht is a nice thought but my rifles are not exactly stock..

The one rifle Bryan is talking about, as am I, is the 22" Valkyrie with a Tight Bore Bartlien, it has a MV with my Cor Bon Load of 2725fps

My Gladius goes 2605fps

My 20" AX goes 2650fps

I am not exactly running slow with a 175gr bullet.

As well I believe there was a discussion about increasing accuracy by banding G7 as well, which shows, while "averages" are good, Bands are Better.

if you note, for a long time now most will say the SMK 175gr has a BC of .505 however anyone who has shot it more than twice knows to .496... same difference.

 

[TiroFijo]

Re: Ballistic coefficient G1 and G7

I've just corresponded with Geoffrey Kolbe, of Border Barrels. He uses a version of McCoy's "McDrag" program in his bullet drag simulator, and states:

<span style="font-weight: bold">"A number of the drag factors depend on the Reynolds number, which will vary with the size of the projectile."</span>

http://www.border-barrels.com/drag.htm

You cannot pretend perfect predictions, but anybody interested can play and see how well (or not) the G1 and G7 fits a given bullet shape.

You can also scale the numbers by a given factor, and see that for a large multiplier (say, a factor of 2 of more) there is a slight BC increase beyond what is predicted by the simple numerical scaling. In othe words, if you have a bullet that is 2x the diameter, the BC increases a bit more than two times.

No doubt the G7 (or G5) drag model will have a better than the G1 <span style="font-style: italic">for bullets that closely match their shape</span>, but you may be surprised with some other shapes, as shown by the calculator.

 

[Radioactive Yeti]

Re: Ballistic coefficient G1 and G7

This definitely needs to be a sticky... Some of the best info I have found online about ballistic modeling. Thanks guys.