Range Report A comparison of ballistic programs vs actual Dope

[ReaperDriver]

OK guys, I got together with some friends on friday for my long-awaited 1K yd desert steel shoot with my .308 SPS-Tactical. I started off over the previous weeks tweaking my "honey loads" and making sure I had good chrono data and dope for as far out as I could get on the range. I have three loads I worked up that were really shooting well out to 500m (550yds) and 875-900 yds and I was itching to try them out at 1K. My loads were 168 AMAX (2690), 178 AMAX (2590) and 175 SMK (2610). I also had just shot the loads two days prior to confirm my 100 yd zero and it was spot on.

I also have both Ballistic FTE and KAC Bulletflight on my iphone and I was hoping to be very close to on target with my 1st shot at 1K, hoping that would be within 0.1 or 0.2 Mils using the ballistic computer data. Up to know I have prefered the Ballistic FTE over KAC Bulletflight, mainly because of the more user customizable features in Ballistic. Anyway, I plugged in the data for the conditions as follows (downloaded from Ballstic's WX function):

Range - 1000 yds (lasered)
Temp - 50F
Alt - 4200 ASL
Baro pressure - 25.65 (standardized)
Humidity - 20%
Wind - ~ 10 mph from 9 o'clock
LOS angle: -7 degs downhill

I started out with the 168 AMAXs, since they had shot very well at 900 yds a few weeks back. I dialed in 9.1 Mils up and 3.1 mils left based on Ballistic FTEs output and let her fly. Spotted round was a FULL 2 mils low and 2 mils left. I was thinking WTF??? How could it be that far off? I was pretty sure I didn't pull it. So I dialed the correction in and by the 3rd round I had the elevation down very close, but the gusting winds were kicking my ass in the horizontal. I ended up at about 10.9-11.0 mils up. So I tried the 175 SMKs and 178 AMAXs next and this time ignored Ballistic FTE's data it was telling me (9.6) and went with 11.2 and was within .1 to .2 mils of being dead on in elev and was getting hits on the steel plate depending on how much the wind fluctuated. But about 11.2-11.4 mils up was holding the vertical very well at 1K and misses on the 1/2 MOA wide steel plate were mainly due to wind fluctuations. My spotters said the gun was holding the elevation very well all day once I got it dialed in.

So.... I was really racking my brains trying to figure out why I was so far off and I spent several hours this afternoon on a lazy sunday on the couch running all my data that I saw on friday against other programs to see if I could see any glaring errors either in my input data or in Ballistic's output. So I compared identical input data I put into FTE against KAC's Bulletflight and JBM from their website (both the "trajectory - Drift" and the Trajectory - simplified"). I found some interesting results compared to my actual Dope. One of the 1st things I found was the auto download for the weather conditions on Ballistic FTE will give some serious errors when using the Barometric pressure function with "standardize pressure" button ON. When the weather downloads, I get strange barometric pressures like 27.59" hg. That is an abnormally low pressure reading and it accounted for the inital error. That was the primary reason why I started off more than 2 mils off at 1K yds. When I download the weather from KAC Bulletflight at the exact same time, I get more reasonable baro readings of 30.03. When I set the Ballistic FTE to more the more reasonable baro settings, I get more normal mil settings. So I re-ran all the comparison numbers to the standard ICAO pressure of 29.92 to keep all the data the same. I still found some decent discrepancies from my observed dope. Here's what I found:

168 AMAX / 1000 yds
.475 G1 BC / .230 G7 BC
Actual Dope: 11.1 mils
Ballistic FTE: G1 - 9.8 G7 - 10.1
KAC Bullet Flight G1 - 10.0 G7 - 10.3
JBM Drift G1 - 9.8 G7 - 10.1
JBM Simple G1 - 10.7 G7 - 11.0

178 AMAX / 1000 yds
.495 G1 BC / .240 G7 BC
Actual Dope: 11.5 mils
Ballistic FTE: G1 - 10.4 G7 - 10.7
KAC Bullet Flight G1 - 10.6 G7 - 11.0
JBM Drift G1 - 10.4 G7 - 10.4
JBM Simple G1 - 10.7 G7 - 11.0

175 SMK / 1000 yds
Auto G1 BC / .243 G7 BC
Actual Dope: 11.4 mils
Ballistic FTE: G1 - 10.2 G7 - 10.4
KAC Bullet Flight G1 - 10.6 G7 - 10.7
JBM Drift G1 - 10.2 G7 - 10.4
JBM Simple G1 - 11.5 G7 - 11.7

Couple of observations/questions before I wrap up this novel (sorry about that): 1) As far as iphone apps - KAC appears to be a bit more accurate to my observed dope than Ballistic FTE. 2) The JBM simple model seems to be more accurate than the more involved spin drift model at least as far as drop goes and the most accurate of all the 4 ballistic models I tried. 3) G7 BC is better than a single number G1 BC, but the Sierra Multiple number G1 seems more accurate than the G7 for the 175 SMK. 4) I can't understand the gross inaccuracy of the Ballistic calculations when you allow it to use the downloaded baro pressure. It was a full 2+ mils off of actual. 5) No gucci ballistic program replaces actually shooting the gun at range and in varying conditions to gather the real dope.

Any thoughts or similar experiences from other users of these programs? Especially the several here that are ballistic guru's, I'm interested in understanding how all these factors fit together.

 

[sobrbiker883]

Re: A comparison of ballistic programs vs actual Dope

What chronograph did you use to get you data?

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: sobrbiker883</div><div class="ubbcode-body">What chronograph did you use to get you data?
</div></div>

CED M2. I chrono'd the same 3 loads probably at least 3 times over different temps, starting in the low 80s and finally down in the low 60's. Using RL-15, I was not seeing a significant difference in velocities. Granted I shot at 50F on this particular day that probably accounts for a bit of the inconsistancy of computed vs actual dope. But what was surprising was how much the different programs varied from each other using the exact same input data.

 

[Lowlight]

Re: A comparison of ballistic programs vs actual Dope

I'll bet it was your LOS angle that was wrong causing everything to go low... it probably wasn't what you thought it was, and the programs were calculating for the angle that really wasn't there.

My guess is, it wasn't so much the programs as the program driver.

 

[Lowlight]

Re: A comparison of ballistic programs vs actual Dope

If you run a 175gr SMK going 2610fps at altitude there is no way you get 11.4 mils, so either your altitude was off, or your MV is off by 100fps, because 2510fps will give you 11.4 mils using JBM simplified at 25.65 baro.

At 4200ft 11.4 mils is moving slow, you should easily be in the 10s

I use just about any program, JBM, Ballistics, Bulletflight, Loadbase, FFS, and NF Exbal and I am usually within .2 of a mil to what I need, but I don't get fancy with it. It looks to be an error in atmospherics and MV because a 175gr SMK is pretty easy to dope.

We used the Bullet flight and Ballistics last week at Thunder Ranch with M24s and M110s and we had no trouble with either. In fact the soldiers remarked how accurate the programs were.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lowlight</div><div class="ubbcode-body">If you run a 175gr SMK going 2610fps at altitude there is no way you get 11.4 mils, so either your altitude was off, or your MV is off by 100fps, because 2510fps will give you 11.4 mils using JBM simplified at 25.65 baro.

At 4200ft 11.4 mils is moving slow, you should easily be in the 10s

I use just about any program, JBM, Ballistics, Bulletflight, Loadbase, FFS, and NF Exbal and I am usually within .2 of a mil to what I need, but I don't get fancy with it. It looks to be an error in atmospherics and MV because a 175gr SMK is pretty easy to dope.

We used the Bullet flight and Ballistics last week at Thunder Ranch with M24s and M110s and we had no trouble with either. In fact the soldiers remarked how accurate the programs were. </div></div>

That was my point with the baro pressure being wrong on ballistic. I know the chrono data is good. I shot at least one of the loads across an Ohler and it was within <20 fps of my CED. When I re-ran all the loads using a more normal baro pressure - they start getting closer to what my actual dope was.

To give you an idea - Barometric pressure is the best measure of a hurricane's power (the lower #, the stronger) and Hurricane Katrina only measured down to 27.11. So there was no WAY I was getting 25.65 in the NV desert on a clear fall day.

ETA - the LOS angle was measured using the iphone angle measurement feature in Ballistic FTE. I had my friend put his rifle on the target and once he was steady with a bipod and sandbag rear - I laid the iphone on his barrel to get it steady. I forget my HS trigonometry - but the shooting elev was 4200' and the target was at ~3850' at exactly 1000 yds. If someone wants to do the math - I'd be interested in how close to -7 degs it was.

ETA2: I'm not saying the programs are not accurate - I'm trying to figure out where the input error is. But regardless, I ran a test to compare all of the listed programs using the exact same data and there were some pretty large discrepancies between them, aside from not matching my dope. I'm trying to figure out which is most accurate.

Of most concern is why the JBM-simplified and the JBM-drift calcs vary that much in drop #s? I just don't see any input fields on the drift version that would account for that big a drop difference.

 

[Tomcat088]

Re: A comparison of ballistic programs vs actual Dope

I'm not much of a program driver, but I did run the numbers for the elevation difference that you mention. If they are correct, I believe this is what you would get. There would be a different of 50ft from your height to the target height. Then you ranged the target at 1,000 yards, which would be 3,000 ft in length. On a triangle this makes the Opposite side of the angle 350 and the base 3,000; to find the angle you just do arctan(350/3,000) , which is opposite over adjacent. This gave me a result of 6.65443 degrees obviously in the downward direction (-6.65443). I'm not sure how much of a difference it would make, but try entering that value or one close to it and see what your numbers show up as. Hopefully my math is correct, it's pretty late and I'm tired.

 

[Skyking]

Re: A comparison of ballistic programs vs actual Dope

Well i don't know much but i will you my two cents. I am just getting into this too. My few suggestions would be. Use only one ballistic program and forget the others. You will drive yourself crazy going back and forth. I have the Nightforce and Knight Bullet flight and use Jbm as well. Just use one forget about the others. I just use the Bullet flight now on my itouch. Second if you have your real shooting dope for 550 and 900 yards then tweak your program to match up with those for now. By doing that i think you will see better number for 1000 yards.
Next i think you are getting screwed up with the Baro pressure thing. If you down loaded it from local WX with the BulletFlight sofware. It is going to give you pressure corrected for altitude. The standard ICAO in the 29.92 neighborhood. When you get a reading like this, you then put in your altitude in the ballistic program. 4200ft and 30.03. BullerFlight will only let you enter ICAO pressure. 29.92 range. If you have a program that lets you enter station pressure, or i think you use the term "standardize pressure" It would be in that 27.59 range and lower. This is pressure not corrected for altitude. If you use this feature do not put in an altitude. Put in an altitude of zero.

I live at 4500ft asl. Right now i am getting a station pressure of 25.62 from my Kestrel 3500. My ICAO Baro pressure is 29.95.I hope this helps and make's 2 cents.

 

[Skyking]

Re: A comparison of ballistic programs vs actual Dope

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Baro/

 

[AshesToAshes]

Re: A comparison of ballistic programs vs actual Dope

Ballistic and Ballistic FTE as of version 2.0 both use the JBM engine as its core, so you should see identical results between the two.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">To give you an idea - Barometric pressure is the best measure of a hurricane's power (the lower #, the stronger) and Hurricane Katrina only measured down to 27.11. So there was no WAY I was getting 25.65 in the NV desert on a clear fall day.</div></div>

The BP you noted for Katrina was measured at sea level. You were not shooting at sea level.

If the sea-level referenced barometric pressure was actually 30.03, then at 4200 feet, the actual station pressure was probably close to 25.8. You appear not to understand the distinction between barometric pressure (referenced to sea level) and station pressure. Another responder already referenced my web page, but you might benefit from reading it.

http://www.arcanamavens.com/LBSFiles/Shooting/Downloads/Baro/

You don't appear to know where the BP readings you were getting were coming from, and there may be a significant difference between the elevation of where those were measured and where you were.

For that reason, you might want to invest in a way to measure your station pressure. Some people use a Kestrel for that, but I find the pressure sensor in my Casio Pathfinder watch is sufficient.

I ran the trig on your slope data, and got 6.65 degrees.

I ran your data for the 175 SMK through Bryan Litz's ballistic program, using the G7 BC, and my sight height of 1.75 inches. I used 25.8" as the station pressure. With the angle calculation, it gave a prediction of 10.5 mils. Without the angle calculation, it gave a prediction of 10.6 mils, so you can see that the angle is not significant.

Field Firing Solutions, using the same data and a G1 BC gave me a prediction of 10.8 without the angle, and 10.7 with it.

I have two recommendations.

Get a station pressure sensor, so you'll know what the pressure really is where you are shooting.

Once you have done that, and have good field data at 1000 yards with an accurate station pressure, adjust the BC of the bullet in whatever program you want to use to match your field data.

And remember the old saying: "A man with one watch knows what time it is. A man with two watches is never sure."

A ballistic program can never give you precise predictions - there are two many variables. For a list of why not, see this post of mine:

http://www.snipershide.com/forum/ubbthre...771#Post1461771

It's a place to start. Believe the bullet, watch the first round impact, and correct as necessary.

Added: And check the calibration of your scope clicks. If you don't know how to do that, see:

Optically Checking Rifle Scopes

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

Thanks Lindy and Skyking and everyone. You are absolutely correct - I was using station pressure incorrectly. I was using the known MSL altitude of the target and using the downloaded "station pressure". That makes sense that station pressure doesn't use altitude but my brain just didn't work that way. As a pilot - all I've ever used is barometric pressure (referenced to 29.92) and I literally deal with that every day. "Station Pressure" is/was a foreign concept to me and I'm not sure I still quite understand the difference. After running the various programs (Ballistic FTE, Bulletflight, JBM) using standard 29.92 AND including altitude - I came close to the real dope. I think I'l go back and try to use my 25.65 and leave the elevation 0 and see what I get.

What's confusing to me is that the weather download feature of Ballistic apparently uses "station pressure" (25.xx) and KAC Bulletflight uses barometric pressure (29.92, 30.03, etc).

So if I understand this correctly - if I use station pressure, I need to leave the target elevation zero and if I use baro pressure - then I add in the elevation? I think what's fucked up about the auto weather download feature on Ballistic FTE is that it also grabs the GPS altitude of the iphone and includes that in the "current Atmosphere" fields along with a "barometric pressure field (that appears to be "Station pressure"). If I leave the "standardize Pressure" button ON - it puts in the station pressure (27.595 for example) but greys the pressure reading out. If I manually turn the "standardize" button OFF, it appears that I have to manually change the 27.595 to something more like 30.16 to be accurate. So should I leave the standardize button ON and if so what is it doing? Is it ignoring the Altitude that it fills in from the GPS? Here are some screen shots from right now on both the Ballistic FTE and the KAC to show what I'm talking about:

Auto download Weather from Ballistic

Results

Same thing but with Standardize button OFF and normal Baro pressure entered:

Results

Same data but using the KAC program (KAC downloaded the Weather using the actual current baro pressure 30.16):

edit to add: If I use JBM on the laptop - does it want station pressure or baro pressure?

 

[AshesToAshes]

Re: A comparison of ballistic programs vs actual Dope

When "Standardize Pressure" is on in Ballistic, Ballistic "guestimates" pressure to the standard-pressure-at-altitude. It's got nothing to do with current conditions. When it's off, the value you type in should be barometric pressure.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: AshesToAshes</div><div class="ubbcode-body">When "Standardize Pressure" is on in Ballistic, Ballistic "guestimates" pressure to the standard-pressure-at-altitude. It's got nothing to do with current conditions. When it's off, the value you type in should be barometric pressure. </div></div>

AHHHH, that makes more sense. I guess its using a guess based on temp and altitude. So I assume if I want actual baro pressure, I have to go find it from another source on line (assuming I don't have a kestrel) and then manually input that number into Ballistic. Thats a PITA, Since it gets other weather info, I wonder why its not also getting a baro pressure from the nearest weather station??? KAC does get the baro pressure readout when it downloads the weather on line - so maybe I'll start using that one instead.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I guess its using a guess based on temp and altitude.</div></div>

Probably just the altitude. It's not a guess, though, but a calculation based on how much the standard atmospheric pressure declines as altitude increases.

Pressure declines <span style="font-style: italic">approximately</span> one inch of mercury per thousand feet of elevation gain. It's not linear, though - it's gets significantly less at higher altitudes.

If you're going to get the barometric pressure from a non-local source, like off the Internet, the source needs to be close to you, <span style="font-weight: bold">and</span> you need to know your local altitude and that of the source.

For example, I spend summers near Creede, Colorado. The nearest airport is Alamosa. But the field elevation at Alamosa is 7539 feet, and Creede is more than a thousand feet higher - just over 8600 feet where we are.

So, if your program automatically downloads both the altitude and the pressure from Alamosa, it's going to be a full inch of mercury off. If I correctly enter the Creede altitude, though, and it computes the standard atmospheric pressure from the Alamosa BP, it will be pretty close.

And, reference your earlier question, station pressure is the actual local atmospheric pressure. If the BP referenced to sea level is 29.92 inches, then the station pressure in Creede is nearer to 21.6 inches.

The reason you dial your aircraft altimeter to 29.92 when you go above 18,000 feet is so that all aircraft are using the same altitude reference. The absolute altitude may be wrong, because the barometric pressure is probably not 29.92 - but if all the aircraft are using the same reference, they'll all be wrong in the same direction, which prevents conflicts.

When you descend to land, though, the ATC or tower gives you the local sea-level-equivalent BP, so that your altimeter will be accurate with respect to the ground.

I recommend you figure out how to operate one of those programs, and ignore the other, at least until you have a better idea of what you are doing.

 

[azimutha]

Re: A comparison of ballistic programs vs actual Dope

I use JBM and Ballistic 2.0.1 and they totally agree. I switched Ballistic over to using the JBM engine, also chose USMC as the Mil-dot Spec and have always set the Zero Atmosphere to match the Current Atmosphere, which I set this way to match JBM (where I always use corrected pressures):

(BTW, you can screenshot off an iPhone or Touch really easily by holding down the top button and then push the on/off button)

Now I really like Ballistic. The author, Jonathan Zdziarski, has made many thoughtful improvements over time. He even included a request I made in 2.0.1 to round results to tenths or hundredths. (I like 13.4 mils better than 134 1/10ths for no real rational reason).

 

[blackwidow2912]

Re: A comparison of ballistic programs vs actual Dope

i have the bulletflight on my ipod touch and nothing was matching up. untill my buddy told me to put the alt. to 0 and put in the baro. from my wind meter. as long as my angle is correct, temp, hum. are all in its right on all the time. try it it works...

 

[308sako]

Re: A comparison of ballistic programs vs actual Dope

Deleted in protest!

 

[308sako]

Re: A comparison of ballistic programs vs actual Dope

Deleted in protest!

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

As I noted above, the angle is insignificant - 0.1 mil difference between the angle indicated and a flat shot.

More probably the error was in the range to the target. A range error of 20 yards is worth about 0.5 mil at 1000 yards with a .308.

Lots of room for errors in a shot that long. This question comes up often enough that I sat down and wrote a web page about it today. See:

Sources of Ballistic Program Inaccuracies

 

[308sako]

Re: A comparison of ballistic programs vs actual Dope

Deleted in protest!

 

[Lowlight]

Re: A comparison of ballistic programs vs actual Dope

Sounds like I said, a whole lot of operator error... the program wasn't wrong, the person inputting the data was...

with any computer programs, garbage in always equals garbage out.

 

[308sako]

Re: A comparison of ballistic programs vs actual Dope

Deleted in protest!

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The operator was trying really hard to do right.</div></div>

I have no doubt of that. These discussions illuminate what frustrates many shooters trying to work at extended distances.

When someone says that their ballistic program was "right on at 1000 yards", I generally conclude that if they are telling the truth, they were lucky enough to have offsetting errors.

 

[308sako]

Re: A comparison of ballistic programs vs actual Dope

Deleted in protest!

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

Good discussion all and I think my big takeaway is understanding what the correct input data is for baro pressure vs station pressure is and how it effects the final output.

My biggest gripe with these programs, especially the iphone apps is the lack of documentation that explains what data is required and what sources it gets some of its on line downloads from.

Final question that I think got lost in the discussion is: looking at my test results in the OP - can anyone explain why the "JBM simplified" appeared to be quite a bit different than the "JBM -drift" (which is what model Ballistic 2.0 uses). Not only was it different, but the simplified model appeared to have the most accurate data compared to my actual dope.

And Lindy - thanks for the refresher on ATC altimeter setting academics. Kidding - just busting your balls.

Good information on the shooting side of the house.....

 

[DaveV]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"> Sources of Ballistic Program Inaccuracies </div></div>

Outstanding article, Lindy! It's info like this that keeps moving the ball forward for guys like me to wrap our heads around. Thanks for taking time to share your knowledge with us.

 

[One-Eyed Jack]

Re: A comparison of ballistic programs vs actual Dope

I just ran a few JBM calcs, assuming that your station pressure was 25.65" Hg, and compared the results with your reported dope. I live at 4,830' here in NV and our station pressure is very often 25.3", so 25.65" at 4,200' seems about right. To make JBM agree with your data, you would need a station pressure of about 29" Hg, which is extremely unlikely at 4,200' (that would be a world's record high pressure at that alititude**). While your baro pressure may not be correct, there doesn't seem to be a physically reasonable one that brings your data into agreement with JBM.

I scanned a number of other posts but didn't see anyone suggest that you check your scope turret calibration. In particular, I was struck by your 175SMK data which said you needed 11.4 mils at your elevation to get to 1kyd, which seems like a clue - that's just too much, unless your MVs are way off instead.

<span style="font-weight: bold">So, I suggest you check your scope to confirm it's giving you good elevation numbers, and reconfirm your MVs with a different chrono (at the very least, use QuickLoad to see whether you are in the ballpark).</span>

** <span style="font-style: italic">The highest atmospheric pressure ever recorded is 32.06" Hg adjusted to sea level. If a station pressure of 29" at 4,200' were adjusted to sea level, it would be over 34" Hg.</span>

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body">I just ran a few JBM calcs, assuming that your station pressure was 25.65" Hg, and compared the results with your reported dope. I live at 4,830' here in NV and our station pressure is very often 25.3", so 25.65" at 4,200' seems about right. To make JBM agree with your data, you would need a station pressure of about 29" Hg, which is extremely unlikely at 4,200' (that would be a world's record high pressure at that alititude**). While your baro pressure may not be correct, there doesn't seem to be a physically reasonable one that brings your data into agreement with JBM.

I scanned a number of other posts but didn't see anyone suggest that you check your scope turret calibration. In particular, I was struck by your 175SMK data which said you needed 11.4 mils at your elevation to get to 1kyd, which seems like a clue - that's just too much, unless your MVs are way off instead.

<span style="font-weight: bold">So, I suggest you check your scope to confirm it's giving you good elevation numbers, and reconfirm your MVs with a different chrono (at the very least, use QuickLoad to see whether you are in the ballpark).</span>

** <span style="font-style: italic">The highest atmospheric pressure ever recorded is 32.06" Hg adjusted to sea level. If a station pressure of 29" at 4,200' were adjusted to sea level, it would be over 34" Hg.</span> </div></div>
OEJ, out of curiosity - what mil drops are you getting using my conditions from above?

 

[azimutha]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">My biggest gripe with these programs, especially the iphone apps is the lack of documentation that explains what data is required and what sources it gets some of its on line downloads from.
</div></div>

I hear you there. Although I'm a big fan of Ballistic now, it took some dinking around and a few emails to get it to match JBM.

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">
Final question that I think got lost in the discussion is: looking at my test results in the OP - can anyone explain why the "JBM simplified" appeared to be quite a bit different than the "JBM -drift" (which is what model Ballistic 2.0 uses). Not only was it different, but the simplified model appeared to have the most accurate data compared to my actual dope.</div></div>

First of all, I think you can turn drift off in Ballistic. As for some background on it, although I don't think he was the first person to deal with it, AFAIK Bryan Litz appears to have supplied the drift calculation to JBM's author and it was picked up in turn by Ballistic when the new version incorporated the JBM engine option. From reading Litz' book, the theory makes sense. But YMMV. I have yet to really test the difference out at distances where it matters so I have no real data to say use it or not.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ReaperDriver</div><div class="ubbcode-body">
Final question that I think got lost in the discussion is: looking at my test results in the OP - can anyone explain why the "JBM simplified" appeared to be quite a bit different than the "JBM -drift" (which is what model Ballistic 2.0 uses). Not only was it different, but the simplified model appeared to have the most accurate data compared to my actual dope.</div></div>

First of all, I think you can turn drift off in Ballistic. As for some background on it, although I don't think he was the first person to deal with it, AFAIK Bryan Litz appears to have supplied the drift calculation to JBM's author and it was picked up in turn by Ballistic when the new version incorporated the JBM engine option. From reading Litz' book, the theory makes sense. But YMMV. I have yet to really test the difference out at distances where it matters so I have no real data to say use it or not. [/quote]

No, I totally get the whole drift theory and the windage calcs in both Ballistic and JBM (same thing really) are fairly accurate. That's not what I'm talking about though. What I'm saying is that if you run the exact same parameters through the two different models of JBM - the DROPS are different, by quite a bit. Unless I'm missing something a pure 90 deg crosswind should not affect the ballistic drop of the bullet. I get that a headwind or tailwind will affect drop, but I wouldn't think a pure crosswind would. Lindy or others, any thoughts on that?

edit:
<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I hear you there. Although I'm a big fan of Ballistic now, it took some dinking around and a few emails to get it to match JBM.</div></div>
what did you find out via email to do to tweak it?

 

[One-Eyed Jack]

Re: A comparison of ballistic programs vs actual Dope

ReaperDriver, assuming:

* 175SMK
* 2,610 fps MV
* Scope height over bore 2"
* Station (local) pressure 25.65" Hg
* Temp 50F
* Humidity 0%

With these assumptions I get 10.1 mils elevation for 1kyd - a reasonable value. The baro station pressure must be increased to over 29" to get 11.4 mils elevation. Instead, if you decrease your MV to 2,500 fps, you can also get to 11.4 mils while maintaining the rest of the assumptions.

BTW, JBM works and you should be within 0.1-0.2 mils of your range dope if you've used accurate input data. <span style="text-decoration: underline">Check your scope calibration and your MV.</span>

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: One-Eyed Jack</div><div class="ubbcode-body">ReaperDriver, assuming:

* 175SMK
* 2,610 fps MV
* Scope height over bore 2"
* Station (local) pressure 25.65" Hg
* Temp 50F
* Humidity 0%

With these assumptions I get 10.1 mils elevation for 1kyd - a reasonable value. The baro station pressure must be increased to over 29" to get 11.4 mils elevation. Instead, if you decrease your MV to 2,500 fps, you can also get to 11.4 mils while maintaining the rest of the assumptions.

BTW, JBM works and you should be within 0.1-0.2 mils of your range dope if you've used accurate input data. Check your scope calibration and your MV. </div></div>

Try 20% humidity and 1.8 scope height and see if that makes a difference. I suppose its possible and quite probable that my MV was lower than chrono'd given I chrono'd them at about 65-70F and it was 50F the day we shot. But I have a hard time believing I was losing 110fps.

 

[One-Eyed Jack]

Re: A comparison of ballistic programs vs actual Dope

No change with the revised HOB and humidty. At long range, HOB is a tiny correction (0.2"/1000 yard = 0.006 mils) and humidity has very little effect on elevation. A lower HOB would require less elevation, and higher humidity would give you less drag and therefore lower elevation - both corrections are in the wrong direction.

PM me with your 175SMK load information, including the water volume of the fired case (Weigh the fired case with the primer in it, then fill it to the very top with water with a bulging meniscus and weigh it again. Make sure you dry off the outside of the case before weighing it with the water.) Tell me everything you know about the load and I'll run some QuickLoad calcs tonight. Also, tell me what scope and reticle you were using.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

Will do. I'll have to wait until I get home tonight, I'm getting ready to go fly. But thanks - I'm interested to see what you find out with QL.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

Lindy, btw - I went back and caught up on your links. Great reading and info. I appreciate you time and effort! Thanks.

 

[Jeff in TX]

Re: A comparison of ballistic programs vs actual Dope

I read through your data, most of the responses and Low Light helped pick out some what I saw as obivious indicators for your error results.

Ballistic programs can be very helpful and some are extremely accurate, but they’re only as good as the data you feed them.

The G7 coefficient drag model seems to be all the rage these days especially with the help of Bryan Litz, myself and few others getting folks to understand the differences in coefficient drag models and getting them away from using the G1 drag model for everything. However the Sierra matchkings fit the G5 coefficient drag model much better than the G7 since it’s truly not a VLD designed bullet. How did you obtain your G7 BC? If you plucked it from a library that may be an issue also. Different rifles can shoot the same bullet differently and produce different BC’s for the same bullet. They may be close or they could be vastly different. Barrel diameter, twist rate and length are the real factors. You should try measuring your 100 yard velocity and get a good 10 round average. JBM has a quick feature that lets you plug in your muzzle and distant velocity readings and will give you your actual corrected BC. BTW, your measured 100 yard distances “MUST” be very accurate and you cannot rely on a laser range finder. If you’re off, your corrected BC will be off

Your scope height is critical to accurate results but there’s a gotcha involved with this in making your ballistic programs results and one I stumbled on by accident. If your rifle has angled bases it will throw off your ballistic program outputs somewhat. I’ve done extensive testing in the field using lots of live range data and number crunching and with my rifles I’ve found I needed to come down in my scope height by a couple few tenths of what I actually measured.

Last but not least is using barometric pressure or altitude. Pick one and never use both. Using standard readings on a ballistic program is always a receipt for inaccurate results. The most accurate results come from setting your ballistic program at 0’ altitude and using the actual measured barometric pressure. If you try to use both which a lot of ballistic program users do, your two fields with conflict and the results are skewed results.

Hope it helps and best of luck.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Your scope height is critical to accurate results but there’s a gotcha involved with this in making your ballistic programs results and one I stumbled on by accident.</div></div>

Changing the scope height by 0.2 inches results in an elevation prediction change of 0.1 mil on a 1000 yard shot. That's insignificant, and cannot be the result of a slanted base.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">If your rifle has angled bases it will throw off your ballistic program outputs somewhat. I’ve done extensive testing in the field using lots of live range data and number crunching and with my rifles I’ve found I needed to come down in my scope height by a couple few tenths of what I actually measured.</div></div>

The difference between the front and the back of a 20 MOA base which is 5 inches long is about .03 inches.

By changing the scope height in the program, you are likely simply compensating for another inaccuracy.

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The most accurate results come from setting your ballistic program at 0’ altitude and using the actual measured barometric pressure. If you try to use both which a lot of ballistic program users do, your two fields with conflict and the results are skewed results.</div></div>

Absolutely correct.

 

[Jeff in TX]

Re: A comparison of ballistic programs vs actual Dope

Lindy,

I hear what you’re saying when it comes to scope height and 20moa angled bases. I argued with myself…over and over again, did the same calculations and came up with the same conclusions you posted.

A few years back I set out on a quest to get my ballistic program data to accurately predict and match my range data. After a few long days at TacPro spread out at different times of the year collecting range data I started to run some numbers. I had accurately measured my BC from the muzzle, 100 and 200 yards using 10 shot velocity strings averages over my CED Millennium chronographs. Calculated the correct coefficient drag model for the bullets I was shooting.

In the end I could get my 100 and 1000 yards measurements to match perfectly as some of my intermediate ranges. I was having trouble getting my 500 to 800 ranges to match up and this was consistent with all three guns. I tweaked velocity, BC and it would skew my other ranges. I decided to try adjusting my scope height and low and behold my intermediate ranges came into line. This worked for all three rifles. I argued with self over and over it shouldn’t make a difference and have been told by other knowledgeable shooters like you, it would make no difference but it did.

I did a posting of my findings a few years back on this board and few other long range hunting boards. I received a bunch of replies from other folks that by adjusting scope height by a few tenths corrected their intermediate ranges when nothing else worked.

The proof was when I went shooting with a buddy in Colorado, we were shooting at 8000’ in 15 degree weather. After verifying my 100 yard zero I plugged in data to my laptop, adjusted for the conditions and my first shot was at 750 yards. Other than being off 4” right for wind, I hit center mass.

Again, at the surface I agree with what you’re saying, but after doing a lot of testing and number crunching I know what worked.

 

[BryanLitz]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Again, at the surface I agree with what you’re saying, but after doing a lot of testing and number crunching I know what worked.</div></div>

Jeff and Lindy,
When you consider the geometry of a tapered base, the taper has a minor effect on sight height over the length of the base (as Lindy pointed out above). However, if you consider the effect this has on the sight line compared to the bore line <span style="font-style: italic">at the muzzle</span>, it can be more significant. For example, a 20 MOA taper over 36" results in the sight line being 0.19" closer to the bore line at the muzzle than at the action where it's likely to be measured. Could this be the reason why Jeff has to subtract "a few tenths" from his sight height to get the dope to match?

I seem to remember that in one of the JBM trajectory calculators it asks for scope base taper and barrel length with the sight height inputs. When I saw it I thought it was an unnecessary detail but never did the math. Could Jeff's experience be proof that that geometry is significant? I've advised shooters in the past that an angled scope base has no effect on a trajectory prediction. That idea may need revision. Granted it's small, but if Jeff was able to see the discrepancy in his field data, then I consider it 'significant enough'.

As for Jeff's statement that bullets fired from different rifles will fly with different BC's... The information available to me now doesn't necessarily support that. On rare occasions, I've had the opportunity to test bullets from different rifles. More often than not, the results were within 1%. There is one exception to this, and I'm not sure if the difference is real or a result of experimental error.

I'm taking part in some BC testing today with Mid Tompkins at the Ben Avery Range. We'll be measuring the BC's over 1000 yards using chronographs and acoustic sensors. I'm interested to see if the BC's derived from time of flight data match the BC's derived from velocity data. My suspicion is that the G1 BC's will be different for tof vs velocity, and the G7 BC will be 'much less different'. Maybe I'll run a comparison for G5 as well, for Jeff's sake

We'll be focusing on .30 caliber (mostly 155 grain class) Palma bullets and some 6.5mm stuff. We'll be firing similar bullets from different rifles over the same test equipment so we will be able to provide a few more data points to address this question. My current belief is that bullets will fly the same from any 'healthy' barrel, meaning a barrel that's not shot out and provides at least adequate stability to the bullet. There is an exception to this and that's when the bullet slows to transonic. At that point, I believe the twist rate and even the character of the rifling engravings can have a big influence on how the bullet flies at transonic speeds. As always, I stand to be corrected on the belief. There are countless reasons why shooters could 'perceive' a difference in a bullet's trajectory from different rifles, but I think they all come from imperfect knowledge of other variables like scope click value, MV, etc.

BTW Lindy, thanks for another well written reference on trouble shooting ballistic program accuracy.

Regarding the original posters concerns, I think the one thing that has to be answered before anything else can be entertained is weather or not the scope adjustments are verified. This is a fundamental question that has to be answered, otherwise you don't even know what your 'real field data' is.

Take care,
-Bryan

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

Bryan: thanks for the kind words.

I don't regard the scope base issue as significant. Once you zero the rifle at short range, 100 yards or meters, the line of sight is exactly the same as it would be on a flat base, except for the difference in height, which, as I've indicated, is not enough to make any difference.

Certainly there are slight differences in the effective BC of each bullet caused by inconsistencies in the bullet shape. I think most of us shoot enough shots when getting dope, as a rule, to average those out.

I have seen a guy shooting off a bench over a chronograph, who could accurately predict the measured muzzle velocity of a shot by how much shoulder pressure he put on the rifle. That leads me to suspect (a) that people who shot over a chronograph off a bench, and then do their field shooting prone, may have somewhat different muzzle velocities than they think they have, and (b) there are going to be differences in how we shoot on any given day.

As I said in my article, <div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Understand from this discussion that no ballistic program can produce an output sufficiently accurate to guarantee a first-round hit at ranges beyond a few hundred yards. A ballistic program is <span style="font-style: italic">correctly</span> used to get you close to that first-round hit under conditions you don't normally shoot in.</div></div>

I have furnished dope from ballistic calculations over satellite links to guys deployed in very unfamiliar conditions, usually at high altitude in very cold temperatures...

The feedback I got was that the dope got them <span style="font-style: italic">close enough</span> to make the followup shot(s), if it wasn't exact enough for a hit on the first round. I'm happy with that.

And I hope these discussion will give people a sense of what's possible with ballistic programs - and what's not - as well as how to make them more consistent.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

P.S. - and then, of course, there's the <span style="font-style: italic">wind</span>...

 

[Jeff in TX]

Re: A comparison of ballistic programs vs actual Dope

Bryan,

As always thanks for your input and insight. I'll be interested from your desert shooting results.

 

[Brown Dog]

Re: A comparison of ballistic programs vs actual Dope

Wow, just read through the thread, deliciously complicated theories solving the original question.

Hoofbeats and zebras?


The only 'horse' considered appears to be ranging error. I'd offer two more 'horses': vertical wind and light condition (scope refraction).


But, of course, zebras are more interesting

 

[azimutha]

Re: A comparison of ballistic programs vs actual Dope

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">The most accurate results come from setting your ballistic program at 0’ altitude and using the actual measured barometric pressure. If you try to use both which a lot of ballistic program users do, your two fields will conflict and the results are skewed.</div></div>

Absolutely correct.
</div></div>

I'm somewhat confused by this. Do you mean by "actual measured barometric pressure" the station pressure or the corrected pressure? My understanding of barometric pressure is that station pressure A @ altitude B is the same as corrected pressure C @ altitude 0, e.g. 811.49mb@1829m = 1013.20mb@0m (sea level). So it would seem to me that I should enter the actual altitude along with the uncorrected pressure or use the corrected pressure at 0 altitude.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

"Corrected pressure" is a term without an established meaning.

If you have where you are shooting a pressure meter which measures absolute pressure, what it's measuring is referred to as the station pressure.

Entering the station pressure, the local temperature, and the local relative humidity into a ballistic program, if you have one in the field, will ensure the maximum accuracy of the air density calculation.

For some additional thoughts on that subject, see Barometric Pressure and Ballistic Software.

For a discussion of terminology, see:

http://wahiduddin.net/calc/pressure.htm

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

Actual field dope is certainly preferable to calculated dope.

People who have to make shots in conditions and/or at distances they do not have field dope for, though, may need to rely on ballistic programs.

A shooter who can "tune" a ballistic program to agree with his field results has a better chance under those conditions.

 

[azimutha]

Re: A comparison of ballistic programs vs actual Dope

Thanks for the links, Lindy. While I would try to use the station pressure w/zero, there are a couple reasons why I can see using corrected pressure. For example, I wanted output that more or less averaged the typical conditions when I'm hunting. (I've also found a spot where I can shoot out to 800 yards at that altitude). Those conditions are as follows:

avg. temp: 40F
avg. hum: 50%
avg. alt: 6000'
avg. corrected pressure: 30.06 Hg (this was obtained from NOAA for a 30-year period)

I realize this is all ballpark, but am just trying to minimize the garbage in, garbage out. Even an approximation should have as good data as possible. One thing I'm finding is that there really doesn't seem to be an appreciable difference between using station pressure w/zero altitude and corrected pressure @ altitude X. If I convert that to mb (hPa) and use 1828.8 meters, 1018 mb, and check "Pressure is Corrected" in JBM, I get a drop of 589.7" @ 1200 yards. vs. 0 meters, 815.352 mb, and unchecked "Pressure..." which is 589.4".

Incidentally, using similar settings in Ballistic, I get 586.9" vs. 586.6" @ 1200 yards.

If I had access to a handheld weather station, I would of course use that with the station pressure. But even when not employing some ballpark average like I outlined above, often the only pressure reading you can get is from the nearest airport or weather station. It's good to know that if you know the altitude where you're going - along with the temperature and humidity, you can use the corrected pressure and get almost the same results. Obviously the results are still probably going to be off since your location may have a different pressure. Where I live, the airport is in the middle of the driest part of the valley floor and I've been in the mountains 15 miles away where it has been snowing all day.

 

[Lindy]

Re: A comparison of ballistic programs vs actual Dope

Yeah, I spend the summers in Creede, Colorado. The nearest airport is Alamosa, which is 63 miles away, and a thousand feet lower. I carry my own pressure instrument.

 

[ReaperDriver]

Re: A comparison of ballistic programs vs actual Dope

Lindy, short of carrying a handheld Kestral WX station - what websites do you know of that give actual station pressure? I've been searching and all so far come back with baro pressure, i.e. altimeter settings. If that is all I'm able to get - If I read your info correctly - then I DO have to input the current elevation of where I'm at for it to calculate correctly, right?

The reason I ask is because I have an airport within about 10-15 miles and about 800-900 feet of where I do my 1000 yard shooting and I can get pretty current altimeter settings. How would you handle that?