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A bif offtopic. Long-range ballistics

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/09/2007 at 21:41
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This is a bit offtopic, but might be of interest to long-range shooters out there with tactical scopes.

I had recently came to conclusion that majority of companies out there offering ballistics software for "civilian" use really don't get it when it comes to long-range shooting.

I had looked at QuickLoad/Target, RSI Shooting Lab, Sierra and some others (names of which I already don't remember)

Pretty much all of them are designed to be used around ancient Mayevski/Ingalls formulas and tables, even though some are designed to use two or even three different Ballistic Coefficient values, essentially admitting that BC is quite useless for modern VLD bullets while still pretty much ignoring  additional science and information accumulated in the last century.

What's worse, absolute majority create ballistics tables with drop and windage expressed usually only in inches. Some offer column that lists "click" count for "standard MOA" adjustments.
Some programs don't offer metric mode. Practically none really address the needs of long-range shooters, especially those with tactical scopes.

Now, for anyone that uses tactical scopes, especially those with mildot reticles and windage/elevation adjustment knobs graduated in centimeters, rather than minutes of angle, it makes little sense to have a table
which requires additional calculations in the field. This is what software and computers are there for in the first place - to make it simple and easy. Strictly speaking, personally, I see no reason to know how much the bullet drops at 700 meters. Bullet drop information to me is actually quite irrelevant considering that the end result for me is that I need to dial-in correct adjustment. Therefore, adjustment is the only thing I would even care about. So, if the software shows me that the bullet drops 125 centimeters at 500 meters it means I still need to calculate how many clicks to dial-in. I would rather prefer a package that simply shows me - 25 clicks (where 1 click = 1 centimeter @ 100 meters).

I have been looking around for nearly 6 months checking out every software package I could find to see if it makes any sense. I think I found it now. It's called Pejsa Ballistics Software. My particular version is Metric, standard version is in Imperial units. You can get it here http://www.pejsa.com/

As a software itself I think it's pretty good. Simple and efficient. In some cases a little too simple, but it produces exactly what I need and is not based on Mayevski tables.

I haven't had a chance to use/verify its usefullness on the range/field yet. If someone had used it and has some practical information on it, I would be glad to hear it. I only wish they had Metric version for PalmOS too.

One important aspect of the program however is that if you want to be really serious about it, you'd have to go on the range and use TWO chronographs at the same time to create proper ballistics table for your load.

Which brings a question - did anyone have any experience with new CED Millennium 2 chronographs? How about the PVM-21?











Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/10/2007 at 08:53
Mike McDonald View Drop Down
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I really like the way you used all that verbage to disguise the advertisement.

 

Most of the ballistics programs in use  already address the issues you tried to raise, including Sierra.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/10/2007 at 10:22
Dale Clifford View Drop Down
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if JBM doesn't work for you, you're doin something wrong

 

http://www.eskimo.com/~jbm/

 

oh, yea forget-- and its free



Edited by Dale Clifford
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2007 at 01:54
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Mike, nobody is paying me for this, so no, it's not advertisement. Just sharing the information. You don't have to buy it, you know that.

Dale - As far as JBM goes - seems like you're still missing the point. If you want a "drag function" that is largely designed to fit the current reality into tables calculated for some "standard" projectile - then yes, it would work for you. If you want correct table calculated for your particular projectile - drag functions designed for "standard" projectile are about as useful as knowing the maximum speed the Lamborghini can go on the track when deciding on tires you want mounted on it when you launch it to the Moon :)



Edited by spreader
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2007 at 09:47
Dale Clifford View Drop Down
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no I think your missing the point, I don't want to launch a lamborghini anywhere, they're too low and make a really sh*tty off road vehicle. (there is a certain level of practical expectations).  Drop and adjustments is just physics, windage is voodoo. If any program worked for windage it would be "the one".

 

not knocking the program you got, probably as good as any. and if the market would look for it.

 

the use of downrange chronographs to really get into the matter is pretty common,

 

are you familiar with the numerical techniques used in either of the programs? and please elaborate on the "additional science accumulated" I can handle it (no math phobias here usually the computational errors of the mumerical method used will introduce as many errors as a "poor model")

 

I haven't had a chance to use/verify its usefullness on the range/field yet. If someone had used it and has some practical information on it, I would be glad to hear it. I only wish they had Metric version for PalmOS too.

Well I have checked JBM out against field use, (along with alot of other guys) and its pretty good. (not saying yours or others aren"t).

Personally I'm waiting for the one that uses radar to shoot a beam down range measure the windage and temp adjustments feed the signal data back in to chip in the scope and adjust an illuminated vector reticle in polar coordinates all in real time. I;ll work on the lamb. later when e geek gets the polarity on my rail gun fixed.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/11/2007 at 23:01
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Dale,

Glad we agree it's all in physics. That's exactly what puts Pejsa apart from practically any other software. Vast majority of all exterior ballistics software packages out there use mathematical models. Most of which are based on Mayevski/Ingalls. Some use slight modifications, acknowledging the fact that BC is not the holy grail and doesn't produce accurate table. Sierra is a good example - they provide up to three different BCs for each bullet, with BC changing as the velocity changes during the flight. The key however is the concept of BC is a load of BS. Assumption is always that calculating BC relative to standard projectile can be used to accurately predict the flight of a bullet launched from a rifle at a given velocity. This assumption by itself is inaccurate, since the bullet velocity changes during the flight, so does the rotation and naturally air resistance has a significant effect. Practically all software packages that exist don't actually take into account air resistance. There is simply no way for them to do so if they're based on math models that don't take it into account.

Pejsa's formula isn't based on a math model that tries to tie behaviour of one bullet in flight to some "standard projectile" based on tables.
The most unique feature of Pejsa program is that it allows you to take four measurements of velocity for a given bullet (and I'm not talking about taking two measurements, say at muzzle and 100 yards and then firing another around and taking measurement at 200 and 300 yards. You essentially fire a round through four chronographs at once) and it would then calculate what he calls retardation coefficient and use that to calculate the velocity of the bullet through the range you want. You could technically take two pairs of measurements separately, if your ammo is good quality and muzzle velocity plus first downrange pair are within your tolerances.

If you want a full math on this, you can find it in his book (and some of the most important information on his website).

If you take a look at this for example:

http://ultimateriflemen.com/ballistics/longrange.htm

Check the Table I, Pejsa BC 0.56 calculation.

You will see that the results in there are based on BC given to the program and only muzzle velocity known. Zero is 200 yards, air pressure is 29.70 in Hg, 59 degrees, sea level. Chronograph used is unknown, neither is accuracy of that chronograph.

If we are to assume that Mayevski calculation is accurate and velocity at 1200 yards is 1196 feet per second, it would mean that at 1200 yards the bullet would drop 552 inches and 325 inches at 1000 yards (you can verify that with JBM G1).

If we're to assume that Pejsa calculation is correct, then for 1200 yards the bullet drops 577 inches, or 335 inches at 1000 yards.

That's quite a bit of difference and that's even before we try to calculate retardation coefficient.

So, it would be obviously interesting to see how accurate it is in real-world, but so far from what I gather his approach seems to make a lot of sense. Perhaps the single most obvious advantage of Pejsa system is the simplicity of formula, which makes calculations in the field easily possible with just a simple calculator. This might come in very handy.




Edited by spreader
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/12/2007 at 10:25
Dale Clifford View Drop Down
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Thanks for answering back with more detail, that is informative, For my own interest I will check into his papers in depth. Building the flight information from empirical input would be a better method and yes drag coef. are definitely a J factor. It sounds like a curve fitting program, do you know?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/12/2007 at 18:07
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Dale,

As Pejsa likes to say, "there is no Pejsa drag function". You essentially "create" a drag function that fits your particular load/bullet.
So, in a way I guess you could say it's a curve fitting program.

The best way to think about it would be to say that if you know the velocity of the bullet at several distances through the effective range, then Pejsa's method would allow you to calculate with fairly good precision velocity and location (in relation to sight line) of this particular load at any other given distance throughout the flight path. So, it's a custom-fitting suit, unlike Mayevski tables.



Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/13/2007 at 18:23
Mike McDonald View Drop Down
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I'm going to attempt to ask a couple simple questions here from a layman shooters perspective.  I only have 2 degrees so I won't try to compete

 

Posit;

 

A difference of 10 inches at 1200 yards has been cited as exemplary difference between the two fairly well recognized calculation sets.

 

In most programs we can chose a "G" function to model drag within a set of defined parameters.   Pejsa  says to punch in a data number to bend the trajectory to fit the load I'm shooting based on results known.

 

I know from experience that with a 308 winchester at 1100 asl 80 degrees f and 28.65 average station pressure, my bullet moves a full minute of angle at 1000 yards with a station pressure change of 0.05Hg.  I know that a 20% change in humidity will also move my bullet enough to pay attention to.

 

Query;

 

How does Pesja account for change in station pressure?

 

If I have already shot my data, why would I need to risk a downrange chronograph when I already know that JBM, ATRAG and Sierra are within the circular area of probability that is my target, using standard drag function models.?

 

 

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/13/2007 at 20:33
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Mike,

"A difference of 10 inches at 1200 yards has been cited as exemplary difference between the two fairly well recognized calculation sets." - this was only example and using only a more common approach of calculating trajectory based on BC and retardation coefficient n of 0.5. Under real-world conditions Mayevski tables would be off by far more, compared to what you can get with Pejsa approach. Obviously at least in theory, it needs verification in practice (someone must have done it by now). Oh, and if you're saying Pejsa is well-recognized calculation set, then I guess there should be less resistance to accepting his approach :)

When it comes to atmospheric pressure I think most people fail to realize that it's not the pressure that affects the bullet in flight, it's the density of air. It is said that standard atmospheric pressure at sealevel is 29.92 inches. But everyone knows that during the storm or unusually hot day atmospheric pressure would change. The "standard" atmospheric pressure is merely a reference point. A combination of humidity, dew point, temperature and atmospheric pressure would affect the air density, which in turn affects the bullet in flight.

If you use Pejsa program you can enter your altitude there (or just the pressure).

It seems to me that the best approach to account for air density is not to use straight atmospheric pressure (or altitude) readings. Instead, it's much more effective to use density altitude (see this for some references http://www.nkhome.com/knowledgecenter/viewtopic.php?t=225). Then, assuming you're not shooting at an angle and you're not shooting into a heavy fog that lies 500 yards away, the trajectory calculated will be quite accurate. If the air density changes substantially from your shooting location to the  target area the trajectory may differ slightly, but most likely much less than if you were to use straight atmospheric pressure readings. Interestingly enough, Pejsa says that atmospheric pressure itself has far less effect on bullet trajectory than rotation of the Earth. Currently his program doesn't account for it. He mentioned that in next year he will be releasing a new book that will have additional information on the subject. Not sure I want to buy the book just to find those details out, I would hope that new version of software would instead account for this (if needed).


"If I have already shot my data, why would I need to risk a downrange chronograph when I already know that JBM, ATRAG and Sierra are within the circular area of probability that is my target, using standard drag function models.?"

If you're saying that you already know exactly how your bullet flies, then you already got your answer - you don't need chronograph, Pejsa software or even BCs of your bullets. If you can hit the target anywhere within the effective range and you're satisfied with accuracy, then certainly there is no need for anything else. Furthermore, if you're rifle doesn't have sub-MOA accuracy, you may not even see the difference at 1000 yards.

However, if you reload quite a bit and experiment with different powders, bullets and so forth - it gets complicated very quickly. Here is a simple example. Using JBM pick some standard variables and calculate trajectory of a bullet using G1 and only BC of some known Sierra bullet. Then do the same, but this time pick the bullet from drop down list. See the difference in results.

For example, say take the Sierra MatchKing 175gr, 30 caliber bullet, use BC of 0.505, muzzle velocity of 2850fps.

First do a calculation with G1 and use only the BC, don't select the bullet from drop down list. Then run second calculation, this time use the drop-down selection.

You will see that for BC 0.505 at 1000 yards it calculates the drop of -330.3 inches.
Same thing when the bullet is selected from drop down list shows -334.9 inches

What happened here? Well, most likely the calculation from the database uses three difference BCs and adjusts the calculation as the bullet speed drops by using different BC. And therein lies the rub.
What if I'm shooting Lapua 11 gram 30 caliber FMJBT bullet? I only have one reference BC and that means that even if I presume Mayevski table to be valid, I should expect an error of say 4 inches. If my rifle can only maintain 1 MOA accuracy and I'm shooting out to 1000 yards, it means that I may be potentially 14 inches off the target. If my target is 12 inches, that means I will most likely miss and get frustrated trying to hit it. And what if I shoot a bullet for which I have no known BC at all?

So, if Pejsa helps create a more accurate trajectory table for your particular load, your scope reticle doesn't shift during adjustment and UFO with Kucinich on the way to campaigning in Iowa doesn't fly over your shooting range leaving pocket of ultra-dense air in its wake - your chances of hitting the target increase substantially.


Edited by spreader
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/13/2007 at 21:48
Dale Clifford View Drop Down
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the use of empirical  data to create the curves already has the information in them, regardless of the physical parameter name "given to them" and in this method would'nt be necessary. (air density, drag functions). Even with just 4 data pts, and matlab I can get pretty good curve fits.

the problem I have with this type of approach-- it does away with the advantages of math models, the biggest of which is not to need several chronos and the trouble this approach causes. knowing ahead of time that a statistical treatment must be made to JBM allows for some pretty good results. (difference equation approach vs. analytical approach.) most of the differences I have been able to detect from the differences in the programs have been due in part to the use of different methods in the numerical methods and not in the assumptions underlying the inputs. As an example sierra uses 4th order runga kutta, and another popular one on the net uses a straight c+++ difference equation approach which adds quite a bit of error.

a middle ground of a straight simulation approach works very well, simply shoot for groups at different ranges, remove the statistics of the group size, and "curve fit for the bc" that fits the profile. this requires a little more on computer time, (equipment that is up to the shooting and use of a range) and it would be nice if someone would write an optimization program for this. (from here the exact differential equation for that flight could be projected).

somewhere along the line pejsa has to use a change of input to allow "predications" under new circumstances. How is this incorporated into the math formulas?

I would be suprized, due to the complexity, of just coupled linear differential equations of the acceptance of a new principle or methodology (in the shooting community), even though it uses a more straight forward approach.

Off topic a bit but why isn't bullet velocity ever 2433.245 as an example. and how much error do you think the rounding in the registers of chronos causes?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/13/2007 at 21:53
Mike McDonald View Drop Down
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I think you may have made my point.

 

I use station pressure, as does any experienced distance shooter.  Corrected Sea Level is of no value.  We also take into consideration temperature and humidity.

 

 Rotational deflection is an effect considered when shooting from different compass points.  Its magnitude depends on the direction the shot is fired.  Range data is aquired normally from ranges that shoot south to north +/- a degree or so.  Change that data to a north to south shot and you'll get an eye opening experience.  It sounds like Pesja's statement on atmospherics is based on extreme trajectory projectiles like artillery and not shoulder fired weapons ballistics.

 

I'm not saying it's a faulty, or bad program.  I just don't see that there's value added for  the additional work required gathering raw data.  We shooters spend too much time in theoretical process and forget that increased accuracy is a result of actual practice and not screenware.  While such programs have their value, and I'm a proponent of "any decent information is good information"   the added labor is not going to produce data that has real value in the real world inside of 1500 yards.

Conditional variables extant on site are more of a concern. It could serve as a theoretical "What If" tutorial providing some insight into the effects of temperature, direction, etc but the other programs do that as well, and to an acceptable degree of accuracy.

 

Choosing a standard program per example and having to data sets of only 4 inches difference is lost in the noise of postional instability and ability of the shooter to call wind at multiple locations simultaneously in a 2 second span prior to the shot.

 

From experience, 4 inches at 1000 yards is a hard hold.  I've done it often enough to know.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/13/2007 at 22:07
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Dale,

Seems like you're wandering into theoretical discussions without actually reading his papers/books. You should read it if you want to understand his whole system. Then you can decide whether he is right or wrong.

As far as chronographs go - this is why I was asking if anyone has any experience with PVM-21. From what I gather every other consumer chronograph on the market has an error of anywhere between 30fps to 100fps, depending on brand, software used to control it, signal converters and so forth. If we assume "only" 30fps error, it's typically about 10 inches drop at 1000 yards. Quite a lot if you ask me.


Mike,

Don't know what you mean by "Corrected Sea Level". As far as theory versus practice is concerned, it's all really very simple. In theory, there is no difference between theory and practice. In practice - there is.

If you're already so experienced with particular load that you don't need any more ballistics tables, then it doesn't matter to you who uses what method for these calculations and why each method is inaccurate and by how much. If on the other hand you need a way to calculate trajectory to get you close enough without wasting thousands of rounds of ammunition and who knows how many hours - the most accurate formula/system wins. As far as shooting ability goes - that's exactly the point. Your shooting is only as good as the weakest link in the system. And my personal approach is - eliminate all weaknesses in the system, leaving just one - the shooter. I forgot who said this - "only accurate rifles are interesting". That's how I see any software, tool or device as well. I'm not particularly interested in "good enough". I have an interest in "best". So, if Pejsa proves to be "good enough", I will simply move on and find something better. If on the other hand it proves more accurate than anything else in existence - my hat is off to him.





Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 09:31
Dale Clifford View Drop Down
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yes I am hoping you knew to save the reading and analyzing - 10 inchs error in 1000 yd is 10/36000 or one in 1/3600 which is still pretty damn good. but I do agree on the more accuracy (in the models and measuring devices is always good). The biggest problem is the implicit curve is not known for that circumstances. In order to judge pejsa or any method it would have to be computed against that curve either statistically or analytically.

my interest in the theory part is based in your statement -- current scientific technique-- which is ahead quite a ways, of the- lets use what we got now. (not that either is better, people have time constraints and assign priorities accordingly.)

I think the new record of something like 1" with a .338 hulk will open some doors in technique, as for me, I'm still looking for loads with ES less than 10 fps.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 18:38
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Corrected se level is barometric pressure as reported for your location corrected for altitude and humidity.  It's what the weather guys report at 6pm.

Station pressure is what you work from when you're shooting.  Actual pressure where you are, uncorrected.  Corrected sea level only has meaning to a shooter if I'm going to jump into the shooting range.  :)

 

I agree on the theory that a software package is a good thing for newbie shooters as a reference tool.  There are some amazingly sophisticated packages currently employed in Mil use that are a real aid to extreme distance shooting.

 

Having said that I suppose I'm getting into an area of conflict between playing on the computer and actually shooting.

 

 Here's a decent and accurate rule of thumb to stop wasting those hypothetical "thousands of rounds" to gather data;

 

Zero at 100 yards.  5 rounds.

Shoot 200 and measure drop.  That becomes your 200 yard zero.  5 rounds.

Double your 200 yard sero and shoot at 300 yards to confirm.  3 rounds.

Add your 200 and 300 yard data to give 400 yard zero, shoot and confirm.  3 rounds.

Add 300 and 400 yard data to give 500 yard zero, shoot and confirm.  3 rounds.

 

triple 500 yard data and add 10% to get your 1000 yard zero.  Shoot  to confirm.  5 rounds.

 

Eventuially theory has to be cross checked by reality.  I'm guessing that you've shot the Pesja data and found it accurate?  (it is a serious question).

 

 

 

 

 

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 18:42
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mike thanks for that, its good to have something as a quick cross check.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 19:37
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Mike,

Regarding "corrected sea level pressure" - I actually don't see any use for that and I haven't mentioned it, so I'm a bit confused why you brought it up in your original post.
What I was saying is that it makes more sense to use density altitude. Density altitude would describe density of air in your particular location (that is, where you're shooting) using standard reference altitude which you can then use in your calculation to figure out bullet's trajectory.

"I'm guessing that you've shot the Pesja data and found it accurate?  (it is a serious question)" - I think I mentioned that I haven't had the chance to verify it on the range yet, but data itself appears very close to my practical observations, which is the only reason why I'm even talking about it :) If it proves to be just as wrong as other software packages - it goes out the window. It doesn't seem that way though, the theory behind it is pretty solid, unlike Mayevski witchcraft. I should know for sure within few months. This is by the way why I'm spending a lot of time now trying to find any comprehensive reviews of consumer chronographs to find the most accurate model - since if I'm going to use second pair of velocities, it better be accurate, otherwise it will introduce significant error into calculation. I can obviously go with standard value for "n", but in order to verify the theory completely this won't do.

By the way, we could easily arrange for some cross-checks. Next time you're on the range and have the shooting data (bullet weight, known BC, muzzle velocity, temperature, humidity and atmospheric pressure) you can send it to me via email, I can run calculation and we will see how well it matches what you observe in the field.


The sight-in approach you listed would work up to 500 yards (more or less), but out to 1000 yards it will be grossly off (for any caliber that I know).

Federal 175gr 308 Match load with 200 yards zero drops a little over 53 inches at 500 yards (sea-level). For 1000 yards that drop is about 416 inches (potentially more, since it becomes subsonic at about 950 yards). Give this load extra 30fps at muzzle and it drops about 404 inches at 1000 yards. If it is only 30fps under (2570fps in other words), then the drop is 426.5 inches. It gets even better if you substitute 175gr Match King for Lapua LockBase 170gr (official BC of 0.525). Launched at same 2600fps it is still supersonic at 1000 yards and drops 395.6 inches. Give it an extra 30fps and drop is now 385 inches. This is why I'm somewhat obsessed with finding an approach that works best in predicting exact trajectory out to 1000 yards (and beyond if I eventually decide to get 338 Lapua. That would imply finding a 1000+ yard range).

Technically, if you're shooting up to 500 meters, you don't really need ballistics tables. Simple coefficient will do fine. Errors will be so small that they can be considered completely negligible.
Beyond that range things change fast.



Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 19:52
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I forgot to mention. The drop at 1000 yards for Federal 175gr 308 Match load with

300 yard zero is 385.2 inches
400 yard zero is 349.5 inches
500 yard zero is 308.8 inches
600 yard zero is 262.6 inches

as you see it's not a very linear relationship.


Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 21:25
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Well,   I think I'm going to have to agree to disagree with your range data.

 

I shoot 1000 yards every Saturday and have for 10 years now.  Prior to a 10 year layoff, I also shot everyweekend for 15 years at distance.  I occasionallyI run that out to 1800 yards in the field behind my house. 

 

Currently I'm playing with a 175 SMK running 2540fps at 1100asl, 80 degrees f, 37% rh and 28.75Hg station pressure.  It remains supersonic to over 1000 yards, does not keyhole from transonic excursion, printing round holes in paper targets around point of aim.  Come up is 39.00 true moa tested.

This is why I shoot my data.  The sight in data I posted is a rough estimate to get on paper to comfirm actual zero.  I would not ever stand in front of it, it's accurate enough to hunt with.   I use this method for new shooters without prior experience at distance shooting and have found that it works for any 1000 yard capable cartridge from 223 rem to 7stw ( did this one last Sundaymorning.  Sometimes I shoot all weekend non-stop) to the 338 lapua, of which I'm a humble owner.

 

On the chrono, call Ken Oehler  in Austin Tx and ask about the Ballistics lab.  Set it up for 8 foot screen and it's going to be accurate enough that Aberdeen Proving Grounds uses it for really big stuff.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 21:43
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Mike,

Out of curiosity:

1. Did you measure the velocity at 1000 yards? What was _exact_ distance to target?

2. If that was a true 39 MOA, then it is 408.4 inches at 1000 yards ( tan(39/60) * 1000 * 36). What was the zero?

Presuming zero of 200 yards, using Pejsa's program with environmental conditions and MV you indicated, it shows bullet drop of 395.3 inches at 1000 yards and bullet drop of 408.3 inches at 1011 yards.
Bullet does indeed remain supersonic up to about 1140 yards.

So, seems to me - no reason to "agree to disagree". With your input it matches nearly exactly.




Edited by spreader
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/14/2007 at 21:58
Mike McDonald View Drop Down
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I'll try to answer in order;

 

One

No I did not use my M1A to shoot over a chronograph 

Actual distance to target is 1002 yards plus/minus the error of a Lieca range finder.

Down angle was 1 degree.  ES on the load is 9fps, SD is 2

 

Two

Zero range is 100 yards. 

 

regarding the 338 lapua;  Find someplace with a 2200 yard range.  it will impresss you, even with factory 250 grain lapua ammunition.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2007 at 01:22
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Assuming I did my math correctly (I adjusted for humidity manually, since Pejsa software doesn't take it into account directly. I calculated through density altitude with dew point of 51.42 derived from RH of 37% at 80 degrees)  at 1 degree incline for range of 1002 yards and zero at 100 yards I get 408.7 inches.

39 MOA at 1002 yards would be 409.2 inches. Real close.


NOTE: I actually need to double-check my math, since I made an assumption about the way his program works in order to adjust for humidity, need to check with his book what formula he uses when taking altitude, pressure and temperature into account. If I use straight values, without taking humidity into account at all, then it shows the drop of 421 inches.


As far as range for 338 Lapua goes - now you're being mean. My nearby 1000 yard range is about 200 miles away :(
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/15/2007 at 15:46
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As far as math in my previous post (14/November/2007 at 18:22) - ignore it. I made wrong assumption when doing the math for this. The actual formula uses air density when computing the bullet trajectory. So, I was overthinking it, I simply needed to enter the altitude, temperature and pressure and the math is done by a program based on standard reference - the "standard atmospheric pressure at sealevel". So, it calculates the air density based on input (mostly changes in elevation and temperature) and uses that to calculate retardation coefficient, which is then used to compute the trajectory.

One thing I didn't do for the math above is use the program to estimate the BC (since actual retardation coefficient is uknown, because I know only MV. Pejsa doesn't use BC in Mayevski sense). When I calculate the "BC" based on size and shape of bullet, for this particular one it comes up with .513. Then the bullet drop for 1000 yards is 408.4 inches, for 1001 yards 409.5 inches and for 1002 yards it comes up with 410.7 inches.







Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/19/2007 at 08:18
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Do I get master's level class credit if I read this WHOLE thread?  Just curious.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: November/19/2007 at 10:40
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yes and your oral presentation with be the submission, presentation, and defence of the closed form equations (and proof) of why Pejsa is better.
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