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Is BC a drag.......maybe not,is that the problem?


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Most of us who shoot any distances beyond maybe 100y become aware at least of BC-Ballistic Coefficient,a characteristic of bullets that considerably affects their ballistic performance,and becomes crucial as distance increases.

 

There are good Ballistic Engines that predict trajectories using BCs. Brian Litz,eg, has done splendid research refining the appropriate choice of which 'BC' model- eg the G7 is much closer to the BTHP bullet than the G1 based on a flat base bullet.....and Sierra has helped by publishing "BC bands"-BC varies with velocity,so is NOT a constant,and chaanges as velocity slows as distance increases.

 

Many posts here derive from 'problems' of the sort that predictions do not match up t sample shooting,and programs allow for 'tweaking'......whether neccessitated by the programs default settings (eg G7,good but increasingly only an approximation; or inaccurate shooter input-especially 'measured' drop values (.1 inch matters....).

 

OK...so what's new.......

 

HORNADY 4DOF BALLISTIC CALCULATOR

 

DOF? degree of freedom.....an independent variable ......most ("Siacca") BC calculators include only three key static DOFs (range ,windage,elevation) but Hornady's new program incorporates a fourth (the dynamic flight characteristics of the bullet,like yaw,pitch,angle of attack).

 

This is done by the Using "Drag Coefficient (Cd) V Mach value (velocity) " without a BC of any sort.

No BC means that the increasing error induced by the decreasing BC,and crucially it's only approximate match to actual bullets causing increasingly inaccurate drag assumptions,even when G7 is way ahead of G1, even G7 cannot fit every bullet exactly).

 

Hornady's program uses the CdVMach drag curves (derived from Doppler etc) for actual bullets,not a near fit,an exact fit.

 

Hornady's 4DOF ballistics match actual bullet to program exactly,so promise better ballistic solutions (drops that actually match firing.....though ALL the usual accuracies of input must be observed,as always-error in always means 'error' out).

 

Sounds interesting? Indeed, detail on Hornady's website (4DOF Ballistics Calculator).

 

There does not seem to be much/any shooter testing input yet......time will tell,and separate hype from hope.

 

BUT.....

 

Hornady include in their pull down menu mainly bullets of Hornady manufacture (and some Berger, Sierra,Lapua)...at least as yet......so maybe this is one to watch for now....and I don't know about $ either.

Meanwhile,you could check - using Hornady's tech pdf -that you can provide all the input data needed.Seems like the usual stuff....without BC, ('replaced' by Hornady's Drag Coefficient of course-if available for your chosen bullet.)

 

What could go wrong...... other than god,the weather and shooters.... :-)

 

gbal

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There's really nothing new in this. The military have been measuring the actual drag coefficients of projectiles with Doppler radars for years. However I suppose that it is new to see it in the commercial marketplace.

 

UK artillery command post firing solutions used 4DOF computer modelling as far back as the very early 1990s.

Oddly enough, to reduce computing burden the lightweight handheld (AFDC and MFDC) computers, used algorithms that were 'best fit' at different charges and ranges - essentially, it rearward engineered a BC-type firing solution.

With today's computers, Hornady should be offering 6DOF modelling!

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Well there you go. I suppose that it just goes to show that Hornady have a marketing department that enjoys a rather breathless form of hype.

 

http://www.lapua.com/en/customer-center/lapua-ballistics.html

 

Holy crap - that's come on a bit since I last used their data!!! Just downloaded the app - even does 22LR! :) :)

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Well there you go. I suppose that it just goes to show that Hornady have a marketing department that enjoys a rather breathless form of hype.

 

http://www.lapua.com/en/customer-center/lapua-ballistics.html

 

Fabulous resource IF you use Lapua bullets.

 

Is this really a better solution than the ability of, say, Strelock + where you can calibrate the software with actual (measured) bullet drop for a bespoke trajectory table? In theory, I can see why it might be more accurate.

 

At the end of the day, any of these solutions must only be as capable as the accuracy of the information entered, but it does leave me wondering why more manufacturers aren't adopting applications that use drag coefficients via Doppler based solutions. As said, nothing new but I guess requires extensive testing and investment to provide such applications.

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Indeed,my point in opening this post was that Hornady have now released software that does provide 'drag based' alternative to BC based solvers,aand as Shuggy noted,becoming available to general shooters-at a price-is worth being aware of.

Accurate Shooter Bulletin seemed to agree.

Time will tell-all systems depend on scrupulously accurate information input,and I suspect often tend not to get it. So they have the facility to thereafter fine tune/tweak for a closer fit-suck it and see....trial/error.

 

IF the Hornady drag coefficient program does indeed remove one built in source of approximation (the BC-both its 'fit' and far more crucially with G7 at least,it's change with velocity-almost never input-since at best only a general averaging of velocity is possible,and that is another 'approximation' very unlikely to be precise...and only possible with banded G7values IF you are using Sierra values for Sierra bullets.

 

AT least Hornady have seen the potential of this hitherto military system-what is new is realising it should transfer,and operationalising it into a program,for the civilian market. That's the smart bit of interest to civilian shooters(if it works).

gbal

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Interesting read - but starts with Litz explaining that 4 DOF 'isn't a thing' - he's wrong, what he describes as 4 DOF is 4 DOF - the Battlefield Artillery Target Engagement System (BATES) used a 4 DOF ballistic kernel exactly as he describes: MPM plus angle of attack. He seems to be arguing that angle of attack, as a single DOF isn't allowed, and therefore 4 DOF isn't 'a thing'. Well, I suppose it depends on what further calculation one might wish to extrapolate from the 4 DOF prediction

 

(Might mean Hprnady will have a problem getting a patent on 4DOF though - Marconi (or was it RACAL?) were doing 4 DOF in the 80s and 90s. and we spent crap loads on it. More was being spent on BATES at the time than Trident (and BATES was sh1te, its single redeeming feature was the accuracy of its ballistic kernel!)).

 

The nub of the article is correct though, as Shuggy and I have mentioned, there's no new technology on offer in the Hornady offering

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Just did a google on BATES - found an amazingly detailed article:

 

 

It used the modified point mass model with 4 degrees of freedom (also called the Lieske Model after its creator Dr Robert F Lieske of the US Ballistic Research Laboratory). The speed of the calculation was determined by the integration step length, basically the distance between calculations along the trajectory, the shorter the length the more calculating there is for a given trajectory. It calculated a full trajectory for each gun to its individual aimpoint.

 

http://nigelef.tripod.com/fc_computer.htm

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The way I see it is it's all too easy to get absorbed into computer programmes when the thing that most needs work usually is the squidgy fleshy bit holding the rifle ?

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Litz also seems to get rather confused between the verification and validation of a model - they are not the same thing.

 

I have seen a 6DOF small arms simulation (I wish I could remember its name). It was rather impressive seeing the variations in roll, pitch and yaw with range.

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The way I see it is it's all too easy to get absorbed into computer programmes when the thing that most needs work usually is the squidgy fleshy bit holding the rifle ?

Katie price with her kipper lips?

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Litz also seems to get rather confused between the verification and validation of a model - they are not the same thing.

 

I have seen a 6DOF small arms simulation (I wish I could remember its name). It was rather impressive seeing the variations in roll, pitch and yaw with range.

 

Wouldn't that be more specifically, variations in roll, pitch and yaw with variation in velocity? It amounts to the same thing with trajectory as velicity decreases, but the relationship is with velocity and the implications are with trajectory/POI.

 

6DOF is mighty impressive...never come across anything for small arms to that level!

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I think that it is a bit more complicated than that. For example, the 5.56 SS109 bullet has significant yaw variation in the early part of its flight. This is the 'fleet yaw' behaviour that causes significant variation in terminal effectiveness. It's root cause is the inherent variability in each barrel, rather than velocity. It usually damps out after a few hundred metres.

 

The simulation could model both fleet yaw and transonic instability, which I thought was most impressive.

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I think that it is a bit more complicated than that. For example, the 5.56 SS109 bullet has significant yaw variation in the early part of its flight. This is the 'fleet yaw' behaviour that causes significant variation in terminal effectiveness. It's root cause is the inherent variability in each barrel, rather than velocity. It usually damps out after a few hundred metres.

 

The simulation could model both fleet yaw and transonic instability, which I thought was most impressive.

 

Thanks Shuggy. Good points. To have something model that is indeed impressive. How you would go about calibrating that for each barrel is something of a mystery!

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Just looked up Lieske.

 

The Lieske model used MPM with an estimated yaw of repose - an 'average yaw' as the 4th DOF

 

I suppose, if anyone wants to blow the Hornady patent application out of the water, they only need point them towards this (published in 1966!):

 

http://www.dtic.mil/dtic/tr/fulltext/u2/485869.pdf

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Its a big marketing hype, nothing new, something that has been around for years and Hornady being rather naughty suggesting that they come up with the idea!

 

http://appliedballisticsllc.com/Truth%20In%20Performance/Hornady4DOF.pdf

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Spin Doctors-sans Doctorates -often operationalise 'spin drift'-the gradual separation of reality from hype in advertising.

 

Hornady of course may have self inflicted by believing their own claims about deforming Ballistic Tips,which would theoretically change the 'angle of attack' in flight -one key variable in their four degrees of freedom modelling.

 

Old man Joyce H must be spinning in his final backstop,as the company descends into such semantics.

 

"Degrees of freedom' when I first grappled with it in the early 60s was-still is- an important statistical concept,essentially meaning the number of independent variables whose value(s) can be changed,while preserving some synoptic descriptor of the set. ( eg in a set of ten scores,you can change up to nine of them,and preserve the average. Rather loosely considered,that's why five shots are better than three,in terms of confidence in the group size,and only two...or one...well,figure it out....:-)

 

I digress-the concept of 'dof' in lower case can't be trade marked,but the concept is a valuable one,properly deployed as a means of handling complexity,and evaluating data sets.

"Four" might be an simplification for ballistics;when H is available,users will be the test.....hype or hope.

 

Cf bullet drop round 2 thread,post 7.

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