Discrepancy Between Ballistic Calculator Predictions and Real-World Long Range Shots - Seeking Advice

[Justchilln]

Hello fellow marksmen,

I am seeking some insights into a discrepancy I have been experiencing between the predictions of my ballistic calculator (Hornady 4DOF) and my real-world shooting results. I typically shoot at 1000yard range, with a Savage 110 Tactical, Oryx chassis, chambered in 6.5 Creedmoor that’s had about 500-800 rounds of hand loaded Hornady Brass with 41 grains of H4350 for about 2750 fps. Here are the specifics of my setup and the statistics from my shots:

• Rifle: Savage 110 Tactical (6.5 Creedmoor)
• Barrel Twist: 1 in 8”
• Muzzle Velocity: 2750 FPS
• Zero Range: 100 yards
• Sight Height: 2.17 inches
• Axial Form Factor: 1.00
• Bore Diameter: 6.5mm

Shooting Stats (last session):

• Number of Shots: 42
• Max Velocity: 2769 FPS
• Min Velocity: 2737 FPS
• ES: 32
• Avg Velocity: 2750 FPS
• SD: 9.1

I have been meticulous in entering all the relevant data into the Hornady 4DOF and other ballistic apps. However, when shooting at 1000 yards, the calculators suggest an elevation adjustment of 8.24 Mrads, but I find myself needing to dial in 8.7 Mrads to hit the target accurately.

Moreover, I’ve noticed an interesting phenomenon regarding wind effects. When shooting with a 5mph tailwind, the elevation adjustment remains at 8.24 Mrads. However, when shooting into a 5mph headwind, the adjustment changes to 7.90 Mrads, contrary to what I would intuitively expect.

Additionally, I am considering the process of truing my ballistic calculator to my rifle to enhance its accuracy in predicting the necessary adjustments. However, I have noticed that other members of my long range club do not seem to face such discrepancies between their Kestrel ballistic calculators and their rifles. They mostly get on-point predictions with minimal deviations. Is truing a standard practice I should pursue, or might there be other underlying issues with my setup or data entry that could be leading to these discrepancies? I am open to any and all suggestions that could help in narrowing down, rectifying this issue.

I am keen to understand the reasons behind these discrepancies and correct for them to improve my accuracy. I would greatly appreciate

 

[Punkur67]

You need to true your velocity in your calculator. I usually shoot around 800 yards and figure my actual dope. Then adjust your muzzle velocity to get the correct dope for that range. Then go out to 1200-1500 and do the same procedure to true the BC. After that you should be good to go

 

[Bah Bah Black Sheep]

The reason you need more elevation for head wind is it creates more drag on your projectile. Think about a car driving into a good head wind vs a tail wind. I’d verify all your information is in your calculator, we’ve all screwed up on that one before, then true around 800 to get you started. It’s VERY possible the bc is a little less than stated.

 

[Justchilln]

The reason you need more elevation for head wind is it creates more drag on your projectile. Think about a car driving into a good head wind vs a tail wind. I’d verify all your information is in your calculator, we’ve all screwed up on that one before, then true around 800 to get you started. It’s VERY possible the bc is a little less than stated.

Yeah I understand why driving into a headwind would result in higher elevation, that’s why I’m confused , but the opposite is happening. Maybe I’m misunderstanding something with the app but does t the little arrow mean wind direction?

 

[Justchilln]

You need to true your velocity in your calculator. I usually shoot around 800 yards and figure my actual dope. Then adjust your muzzle velocity to get the correct dope for that range. Then go out to 1200-1500 and do the same procedure to true the BC. After that you should be good to go

Ok thanks, I haven’t done any trueing before, will look into SOP for it. Also I don’t really have a 1200-1500 range would my 1000 yard range work as long as I do 800?

 

[FredHammer]

Them dudes using kestrels are on the ball. Barometric pressure is a big deal variable to get exact as possible. Definitely can cause the changes you are seeing if a phone weather app is telling you one baro and a Kestrel is telling you different. The weather app could be pulling data from a long ways from you location, the Kestrel is spot on.

I don't have a Kestrel, but I use two Alt/Baro apps on my phone that syncs gps and gives me the alt. and baro. My watch has alt/barro also and is right there with the apps. So, between 3 daggum baro sources I have it nailed to within .1inhg. I will reduce to just one app here soon, just needed to verify the accuracy.

BC - You didn't specify what bullet you are using, I suspect a Hornady bullet which Hornady has the BC auto calculated in 4DOF. You can also use the general BC calculator in the 4DOF app and enter what Litz has listed or grab BC from a radar chrono that calculates the BC for you as you chrono.

 

[Justchilln]

Them dudes using kestrels are on the ball. Barometric pressure is a big deal variable to get exact as possible. Definitely can cause the changes you are seeing if a phone weather app is telling you one baro and a Kestrel is telling you different. The weather app could be pulling data from a long ways from you location, the Kestrel is spot on.

I don't have a Kestrel, but I use two Alt/Baro apps on my phone that syncs gps and gives me the alt. and baro. My watch has alt/barro also and is right there with the apps. So, between 3 daggum baro sources I have it nailed to within .1inhg. I will reduce to just one app here soon, just needed to verify the accuracy.

BC - You didn't specify what bullet you are using, I suspect a Hornady bullet which Hornady has the BC auto calculated in 4DOF. You can also use the general BC calculator in the 4DOF app and enter what Litz has listed or grab BC from a radar chrono that calculates the BC for you as you chrono.

Thanks for the reply, I manually enter a baro I got from a local civilian weather station but honestly not sure how accurate that and my altitude are.

And yep I’m using Hornady 140 ELDMs so I figured they would be dialed in pretty accurate given it’s Hornadys app.

 

[FredHammer]

Thanks for the reply, I manually enter a baro I got from a local civilian weather station but honestly not sure how accurate that and my altitude are.

And yep I’m using Hornady 140 ELDMs so I figured they would be dialed in pretty accurate given it’s Hornadys app.

I know that is the discrepancy then. I was recently shooting 900yds and my watch baro said 28.6. 4DOF gen calculator had me hitting money waterline for 20 consecutive shots at my elevation dope. I checked the phone weather app for shiggles and it read 30.2. which would have not been good. (Probably the station pressure by watch, and sea level pressure by weather app. Do always use station pressure)

 

[Baron23]

Thanks for the reply, I manually enter a baro I got from a local civilian weather station but honestly not sure how accurate that and my altitude are.

And yep I’m using Hornady 140 ELDMs so I figured they would be dialed in pretty accurate given it’s Hornadys app.

Your local weather station reports barometric pressure which is station pressure adjusted to sea level. Yeah, it can get confusing

Your 4 DOF uses station pressure....this is the actual pressure of the atmosphere where you are standing. Kestrels will provide station pressure. This may be a source of your discrepancy (especially if you're not right down at sea level or darn close) and why the guys with the Kestrels with 4DOF aren't having this issue.

https://kestrelinstruments.com/blog/barometric-pressure-vs-station-pressure-whats-the-difference​

Station pressure changes at various altitudes since it's not adjusted. With barometric pressure, it's the station pressure adjusted to the mean sea level. If the pressure is measured at sea level, station pressure and barometric pressure are equal.​

​

https://www.hornady.com/team-hornady/ballistic-calculators/4dof-ballistic-calculator/instructions​

Pressure: ​

In inches or millimeters of mercury.​

​

NOTE: This is station pressure, from a Kestrel™ or similar – use of National Weather Service [type] data for the area will not be accurate nor is it recommended for use.​

​

https://www.weather.gov/bou/pressure_definitions​

STATION PRESSURE: This is the pressure that is observed at a specific elevation and is the true barometric pressure of a location. It is the pressure exerted by the atmosphere at a point as a result of gravity acting upon the "column" of air that lies directly above the point.​

 

[DownhillFromHere]

OP - here are a few observations on your original question and the posts since.

• You don't specify whether you've collected dope for intermediate ranges sort of 1000 yards. You really should have good data all the way out, preferably every 100 yards, to establish a true trajectory. My experience has been that it's pretty easy to get calculators (Strelok Pro, 4DOF) to provide decent output out to 500 - it's 600 and out that they tend to diverge. Of course, it's the longer ranges where environmental conditions exert the most effect. If your close-in solutions don't match impacts, it's unreasonable to expect the longer ones to be accurate.
• You can adjust ("true") the velocity entered in 4DOF to attempt to match observed POI to solution output. You cannot adjust ("true") Ballistic Coefficient (BC) in 4DOF. People who tell you to true BC have not used 4DOF. The closest you can come to "truing BC" is to tinker with axial form factor, which has built-in limits.
• Baron23 raises a good point with regard to barometric pressure. The pressure reported by weather forecasts on radio, tv, etc is pressure at sea level "under" the reporting station. Example: the station reporting pressure is at 3000 feet above sea level. The pressure reported for that location will be the pressue at sea level "under" the station, not at the station itself. That's what "station pressure" is - the actual pressure where the instrument is located in altitude as well as lat/long, and that's the pressure you have to use in your solver.
• If you haven't done so, watch the Hornady podcast #51, "4DOF Tips and Tricks." They get into pretty deep detail of the whys and wherefores of how the app works. There is a fairly new podcast, #92, that also gets into the weeds but I haven't looked at it all the way through.

With all that said: I still don't trust 4DOF completely because I don't have years of experience with it. I was shooting to 1000 yesterday, and my 4DOF solutions were .3 or so low 800-1000. My 100-yard zero was set and verified on an indoor range (no wind), and I followed the podcast #51 "tips" to the letter.

I'm not blaming the app for inaccurate solutions - rather, I acknowledge my lack of skill in observing conditions which affect where the target appears to be as well as actual trajectory. Seeing the wind behaving a certain way at one range has no bearing whatsoever on what the wind may be doing at a different range, for example... and the 1000-yard range I most frequently use is about as flat as a tabletop so mirage is AWFUL. Search online for time-lapse videos of a fixed-position target taken through a fixed-position camera... and watch te target "move." It's not moving; atmospheric distortion gives the appearance of moving. Objectively, this simply means that the target may not actually be where it appears to be in my scope... and I haven't really gone back and looked at all the dope I've written down to account for lighting conditions in the solutions I get from 4DOF.

 

[FredHammer]

• You can adjust ("true") the velocity entered in 4DOF to attempt to match observed POI to solution output. You cannot adjust ("true") Ballistic Coefficient (BC) in 4DOF. People who tell you to true BC have not used 4DOF. The closest you can come to "truing BC" is to tinker with axial form factor, which has built-in limits.

One can true the BC in the general BC calculator of the 4DOF app.

 

[DownhillFromHere]

One can true the BC in the general BC calculator of the 4DOF app.

You are correct - but then it's a BC calculator, not 4DOF based on radar-measured drag curves. The podcasts speak to this difference.

 

[Justchilln]

Your local weather station reports barometric pressure which is station pressure adjusted to sea level. Yeah, it can get confusing

Your 4 DOF uses station pressure....this is the actual pressure of the atmosphere where you are standing. Kestrels will provide station pressure. This may be a source of your discrepancy (especially if you're not right down at sea level or darn close) and why the guys with the Kestrels with 4DOF aren't having this issue.

https://kestrelinstruments.com/blog/barometric-pressure-vs-station-pressure-whats-the-difference​

Station pressure changes at various altitudes since it's not adjusted. With barometric pressure, it's the station pressure adjusted to the mean sea level. If the pressure is measured at sea level, station pressure and barometric pressure are equal.​

​

https://www.hornady.com/team-hornady/ballistic-calculators/4dof-ballistic-calculator/instructions​

Pressure: ​

In inches or millimeters of mercury.​

​

NOTE: This is station pressure, from a Kestrel™ or similar – use of National Weather Service [type] data for the area will not be accurate nor is it recommended for use.​

​

https://www.weather.gov/bou/pressure_definitions​

STATION PRESSURE: This is the pressure that is observed at a specific elevation and is the true barometric pressure of a location. It is the pressure exerted by the atmosphere at a point as a result of gravity acting upon the "column" of air that lies directly above the point.​

Yeah I understood the difference, I should have been a bit more specific, the baro I was referring to isn’t corrected station pressure. It’s an app that pulls from private citizens weather stations, so I was getting raw pressure readings but they were a few miles away from the range, that’s why I was questioning the accuracy.

 

[FredHammer]

Yeah I understood the difference, I should have been a bit more specific, the baro I was referring to isn’t corrected station pressure. It’s an app that pulls from private citizens weather stations, so I was getting raw pressure readings but they were a few miles away from the range, that’s why I was questioning the accuracy.

I don't know. You might need no less than 3-4 more egg head posts beating this barometric value into you before you understand it.

 

[Justchilln]

OP - here are a few observations on your original question and the posts since.

• You don't specify whether you've collected dope for intermediate ranges sort of 1000 yards. You really should have good data all the way out, preferably every 100 yards, to establish a true trajectory. My experience has been that it's pretty easy to get calculators (Strelok Pro, 4DOF) to provide decent output out to 500 - it's 600 and out that they tend to diverge. Of course, it's the longer ranges where environmental conditions exert the most effect. If your close-in solutions don't match impacts, it's unreasonable to expect the longer ones to be accurate.
• You can adjust ("true") the velocity entered in 4DOF to attempt to match observed POI to solution output. You cannot adjust ("true") Ballistic Coefficient (BC) in 4DOF. People who tell you to true BC have not used 4DOF. The closest you can come to "truing BC" is to tinker with axial form factor, which has built-in limits.
• Baron23 raises a good point with regard to barometric pressure. The pressure reported by weather forecasts on radio, tv, etc is pressure at sea level "under" the reporting station. Example: the station reporting pressure is at 3000 feet above sea level. The pressure reported for that location will be the pressue at sea level "under" the station, not at the station itself. That's what "station pressure" is - the actual pressure where the instrument is located in altitude as well as lat/long, and that's the pressure you have to use in your solver.
• If you haven't done so, watch the Hornady podcast #51, "4DOF Tips and Tricks." They get into pretty deep detail of the whys and wherefores of how the app works. There is a fairly new podcast, #92, that also gets into the weeds but I haven't looked at it all the way through.

With all that said: I still don't trust 4DOF completely because I don't have years of experience with it. I was shooting to 1000 yesterday, and my 4DOF solutions were .3 or so low 800-1000. My 100-yard zero was set and verified on an indoor range (no wind), and I followed the podcast #51 "tips" to the letter.

I'm not blaming the app for inaccurate solutions - rather, I acknowledge my lack of skill in observing conditions which affect where the target appears to be as well as actual trajectory. Seeing the wind behaving a certain way at one range has no bearing whatsoever on what the wind may be doing at a different range, for example... and the 1000-yard range I most frequently use is about as flat as a tabletop so mirage is AWFUL. Search online for time-lapse videos of a fixed-position target taken through a fixed-position camera... and watch te target "move." It's not moving; atmospheric distortion gives the appearance of moving. Objectively, this simply means that the target may not actually be where it appears to be in my scope... and I haven't really gone back and looked at all the dope I've written down to account for lighting conditions in the solutions I get from 4DOF.

Thanks for the observations.

I have DOPE for 100, 200, 350, 500 and it was spot on so what you’re saying makes sense.

As for the station pressure thing, I should have been a bit more specific as I was pulling raw pressure, but location was pretty far away so definitely could have made it inaccurate.

And thanks for info on 4DOF, I’m actually pretty ignorant on how it works so that’s a great resource in understanding the mechanics behind it.

Yeah, trusting any solver seems like it would take quite some time shooting with it, I think my shorterm goal is just understanding why the solution might be off, and just getting more consistent results.

 

[6.5SH]

Thanks for the observations.

I have DOPE for 100, 200, 350, 500 and it was spot on so what you’re saying makes sense.

As for the station pressure thing, I should have been a bit more specific as I was pulling raw pressure, but location was pretty far away so definitely could have made it inaccurate.

And thanks for info on 4DOF, I’m actually pretty ignorant on how it works so that’s a great resource in understanding the mechanics behind it.

Yeah, trusting any solver seems like it would take quite some time shooting with it, I think my shorterm goal is just understanding why the solution might be off, and just getting more consistent results.

If you were using Weather Underground they report Barometer not uncorrected station pressure. The elevation of the reporting station is at the top of each page.
If you go to the History tab for some larger stations the labeling is clearer: Sea Level Pressure (in)

 

[MarcC11B]

Just considering other possibilities, and in response to this:
“I have been meticulous in entering all the relevant data into the Hornady 4DOF and other ballistic apps. However, when shooting at 1000 yards, the calculators suggest an elevation adjustment of 8.24 Mrads, but I find myself needing to dial in 8.7 Mrads to hit the target accurately.”

What scope do you have and have you done a tall target test? Your turret adjustment difference of 8.7 vs 8.24 is about 5%. Not uncommon for scopes to track that much off.

As for this, “Moreover, I’ve noticed an interesting phenomenon regarding wind effects. When shooting with a 5mph tailwind, the elevation adjustment remains at 8.24 Mrads. However, when shooting into a 5mph headwind, the adjustment changes to 7.90 Mrads, contrary to what I would intuitively expect.”
Was this what the 4Dof said or your actual results? Again, this is 95% but the opposite way. Or was it really 8.9 and not the 8.7 you mentioned above. The difference between those two is closer to 98%.

Is the results you describe from 1 day of shooting or are they off consistently?
How many rounds did you shoot in the group to check your zero…don’t they suggest 30-50?