Range Report JBM dope card is screwing with me. Starting to get frustrated! What am I missing!?!

[ScottyD]

I've been struggling with this for a while now. I've been through 2 iPhone apps, loads of JBM print outs, stacks of chrono numbers with a cheap F1, and two scopes (swfa 5-20, and now a kahles 6-24) that have both passed tracking testes with flying colors... I'm shooting 140 A-max in a 25" 6.5cm with 42.4g of H4350. 1.8" scope height. I believe my velocity to be ~2800 fps, but I don't know what to think at this point... My 100yd zero is as good as its going to get...

7000 DA measured with a Kestrel, I go shoot 550yds and get impacts with perfect elevation with 2.8 mils. (JBM gives me a velocity of 2875fps for this)

7000 DA 700yds and I'm centered up at 4.4 mils (JBM tells me my velocity is 2800)

7000 DA 800yds and I'm getting hits with 5.4 mils (JBM tells me my velocity is 2800)

7000 DA 1150yds and I'm confirmed on steel with 10.2 mils (JBM puts me at a velocity of 2725 for this!)

I plug my info into JBM, using the Litz BC for my A-max's, and using a temp of 59 F, humidity 0, and a pressure of 24.25 to generate a 7000 DA dope card -Those numbers come straight from here:

Making Ballistic Cards Using Density Altitude

It says:

"To keep this simple, here are combinations of temperature and pressure that will give you DA steps from -4000 feet to 11,000 feet which you can put directly into your ballistic calculator. Leave the humidity set to zero. If you need other increments or steps outside this range, just use the online calculator.

DA.............Pressure......Temp(F.)
-4000.........29.765........0
-3000.........28.925........0
-2000.........28.106........0
-1000.........27.303........0
0................29.95.........59
1000...........29.055.......59
2000...........28.208.......59
3000...........27.382.......59
4000...........26.573.......59
5000...........25.783.......59
6000...........25.011.......59
7000...........24.257.......59
8000...........23.521.......59
9000...........22.802.......59
10000.........22.099.......59
11000.........21.414.......59


I'm desperate for a dope card that works. A JBM card with a velocity of 2875 had me tracking well to 600yds, then I lose it at 700 and beyond... A JBM card with a velocity of 2800 gets me on at 700-800 but has me missing close shots and long shots... Both 2875 and 2800fps have me missing all day long at 1000+ yds.... Pulling my hair out at this point. Got some big matches coming up and I need to get this sorted out!

Any help or suggestions would be GREATLY appreciated!

 

[BryanLitz]

When I see this problem, the first thing I think of is verifying range.

Here's why; you're spot on at the closer ranges where the targets are within the beam divergence of your LRF. Spot on at 700 and 800 yards with the same trajectory model rules out a lot of things including scope tracking, MV error, etc. But then when you see error at longer ranges, it can be due to uncertainty in range measurement. At 1150 the target is likely smaller than the beam divergence of your LRF, and you might be ranging something else big in the area. It wouldn't take but 30 yards of range error to have the same effect as a 75 fps MV error. It's not hard to miss range your target by 30 yards at 1150. If it's a 'known distance' range, with the target labeled as 1150, this makes range error less likely (assuming those who surveyed the range did it right), but still a possibility.

Not saying this is it for sure, but you asked for suggestions.

Good luck, hope you get it sorted.

-Bryan

 

[damoncali]

Garbage in garbage out. Measure everything. As Bryan said, range is one people don't always think about. But why not measure your velocity as well? In other words, chase the largest uncertainty until it works.

 

[NevadaZielmeister]

I've been struggling with this for a while now. I've been through 2 iPhone apps, loads of JBM print outs, stacks of chrono numbers with a cheap F1, and two scopes (swfa 5-20, and now a kahles 6-24) that have both passed tracking testes with flying colors... I'm shooting 140 A-max in a 25" 6.5cm with 42.4g of H4350. 1.8" scope height. I believe my velocity to be ~2800 fps, but I don't know what to think at this point... My 100yd zero is as good as its going to get...

7000 DA measured with a Kestrel, I go shoot 550yds and get impacts with perfect elevation with 2.8 mils. (JBM gives me a velocity of 2875fps for this)

7000 DA 700yds and I'm centered up at 4.4 mils (JBM tells me my velocity is 2800)

7000 DA 800yds and I'm getting hits with 5.4 mils (JBM tells me my velocity is 2800)

7000 DA 1150yds and I'm confirmed on steel with 10.2 mils (JBM puts me at a velocity of 2725 for this!)

I plug my info into JBM, using the Litz BC for my A-max's, and using a temp of 59 F, humidity 0, and a pressure of 24.25 to generate a 7000 DA dope card -Those numbers come straight from here:

Making Ballistic Cards Using Density Altitude

It says:

"To keep this simple, here are combinations of temperature and pressure that will give you DA steps from -4000 feet to 11,000 feet which you can put directly into your ballistic calculator. Leave the humidity set to zero. If you need other increments or steps outside this range, just use the online calculator.

DA.............Pressure......Temp(F.)
-4000.........29.765........0
-3000.........28.925........0
-2000.........28.106........0
-1000.........27.303........0
0................29.95.........59
1000...........29.055.......59
2000...........28.208.......59
3000...........27.382.......59
4000...........26.573.......59
5000...........25.783.......59
6000...........25.011.......59
7000...........24.257.......59
8000...........23.521.......59
9000...........22.802.......59
10000.........22.099.......59
11000.........21.414.......59


I'm desperate for a dope card that works. A JBM card with a velocity of 2875 had me tracking well to 600yds, then I lose it at 700 and beyond... A JBM card with a velocity of 2800 gets me on at 700-800 but has me missing close shots and long shots... Both 2875 and 2800fps have me missing all day long at 1000+ yds.... Pulling my hair out at this point. Got some big matches coming up and I need to get this sorted out!

Any help or suggestions would be GREATLY appreciated!

I went through the same troubles with my Field Density Altitude Compensators. They worked great out to about 600 meters, then they diverged from true impact points and I completely lost confidence in them. Thus, I kept a data book to be able to try and guess at the longer ranges. It was very frustrating and have hope in knowing that you should get Applied Ballistics, period. With the truing function, you will be able to make up your own data cards. Now realize that when someone as amazing as Bryan Litz helps you out, that you are in good company with that software. Bryan knows more than just about anybody regarding ballistics.

And that is a huge compliment given that throughout history, entire nations have risen and fallen based solely on ballistics.

When I see this problem, the first thing I think of is verifying range.

Here's why; you're spot on at the closer ranges where the targets are within the beam divergence of your LRF. Spot on at 700 and 800 yards with the same trajectory model rules out a lot of things including scope tracking, MV error, etc. But then when you see error at longer ranges, it can be due to uncertainty in range measurement. At 1150 the target is likely smaller than the beam divergence of your LRF, and you might be ranging something else big in the area. It wouldn't take but 30 yards of range error to have the same effect as a 75 fps MV error. It's not hard to miss range your target by 30 yards at 1150. If it's a 'known distance' range, with the target labeled as 1150, this makes range error less likely (assuming those who surveyed the range did it right), but still a possibility.

Not saying this is it for sure, but you asked for suggestions.

Good luck, hope you get it sorted.

-Bryan

Bryan, I cannot believe you did not plug your own software and even your software and Kestrel product. That speaks volumes about your willingness to help others. A good model for a good business.

Can I just say how SUPER happy I am with the Kestrel 4500NV with Applied Ballistics? I have used it about 5 times since getting it last month and once I inputted a trued data point (my hits were only .2 milliradians low at 825 meters), it has been spot on ever since. So much so that I find my need to enter my information into a data book as moot. Seriously. I have ultimate confidence that when I dial in any range down to the nearest meter, I KNOW it will be dead on for elevation. I have used this at my local club matches, as well as a club match in Washington State (Upper Nisqually Rifle Club Practical Rifle Match) and I will be using it at the upcoming Sniper's Hide Cup.

I love the custom bullet curves you created. That was why I opted for the bluetooth model so I could download them for my .308 caliber 155 grain Scenars. I believe that those curves are a lot more accurate than the curves based on approximate G1 and G7 drag models. Thank you for putting so much work into those curves, allowing guys like me the ability to hit anything out past 1000 meters. (1,200 meters was transonic and I do not have enough Drop Scale Factor data to nail those hits down.) Steel really hates me.

Thank you for everything Bryan. My friend and I absolutely love the Kestrel you created. It is the best thing since the rifle scope, in my opinion.

 

[ScottyD]

When I see this problem, the first thing I think of is verifying range.

Here's why; you're spot on at the closer ranges where the targets are within the beam divergence of your LRF. Spot on at 700 and 800 yards with the same trajectory model rules out a lot of things including scope tracking, MV error, etc. But then when you see error at longer ranges, it can be due to uncertainty in range measurement. At 1150 the target is likely smaller than the beam divergence of your LRF, and you might be ranging something else big in the area. It wouldn't take but 30 yards of range error to have the same effect as a 75 fps MV error. It's not hard to miss range your target by 30 yards at 1150. If it's a 'known distance' range, with the target labeled as 1150, this makes range error less likely (assuming those who surveyed the range did it right), but still a possibility.

Not saying this is it for sure, but you asked for suggestions.

Good luck, hope you get it sorted.

-Bryan

Thanks Bryan,

I'm definitely going to give this some more thought, but at this point I have no reason to doubt the ranges. My 550 (500M) came from established berms at a silhouette range, and everything else from a a site-in range and known distance targets at a recent match. The match had a site-in range with established 300, 400, 500, 600 and 700yd targets. These were confirmed by multiple high end range-finders (as well as my own lowly bushnell). I had the bonus of fresh paint on the steel, and saw perfect tracking from 300 to 600, then suddenly my 2875fps card was .4 low at 700. During the match we had known distance targets and I chose the 700, 800, and 1150 targets (1153 actually) as examples. Watching my buddies successfully dial for 1150 with during the match gives me no reason to doubt the range... I will admit it was a generous plate - I would think you could be +/- .1 or .2 and still be on, but my cards are more like +/- 1.5 mils! This leads me towards thinking my best bet may be something with a "truing" function as Nevada suggests...

Thanks again for the help!

 

[ScottyD]

Garbage in garbage out. Measure everything. As Bryan said, range is one people don't always think about. But why not measure your velocity as well? In other words, chase the largest uncertainty until it works.

Thanks for the suggestions Damoncali. I've spent a lot of time in the past shooting my 6.5cm over my f1 Chrony. Never had a reason to doubt it until my dope went all wonky on me. I had been trying to chrono over a big range of temps to track any velocity shifts with my loads. The F1 has shown me a low of 2790 in the cold (20-30F) and a high of 2810 in the heat (80F) -makes me think that H4350 is good stuff! I've been shooting at 60-70F with a DA of 7000 for the recent data I'm sharing with you guys... I've had many more experienced shooters tell me to basically throw the chrony away and just go shoot and generate a card based on your actual POI... So that's what I've been working on lately...
But I hear what you're saying about "garbage in garbage out". Still trying to pin-point where my "garbage" is coming from!

 

[ScottyD]

I went through the same troubles with my Field Density Altitude Compensators. They worked great out to about 600 meters, then they diverged from true impact points and I completely lost confidence in them. Thus, I kept a data book to be able to try and guess at the longer ranges. It was very frustrating and have hope in knowing that you should get Applied Ballistics, period. With the truing function, you will be able to make up your own data cards. Now realize that when someone as amazing as Bryan Litz helps you out, that you are in good company with that software. Bryan knows more than just about anybody regarding ballistics.

Hi NevadaZielmeister! Thanks for the help. This idea of a truing function sounds good to me (although my numbers are such a mess, I worry I could cause a crash when I put my data in! haha). I just bought a Kestrel 4000 (hoping that a solid DA reading would clear up my issues), I'd hate to have to go get an even more expensive one now. Plus I wrongly decided to blame my SWFA scope for a while there, and used that as an excuse to buy the Kahles. So I'm kinda digging myself a hole right now. Haha... I need to get more familiar with the Applied Ballistics programs. Is it correct they are only available in the Kestrel? Does it allow you to print up an actual card so you're not fiddling with electronics during a match? Are there any other options to access a ballistics program with a truing function? I hear what you're saying about Mr. Litz -nothing but respect from me. I'd be happy to support his products any way I can, but $600 for a new Kestrel may not be an option for me at the moment. I'm also headed for the Cup in couple weeks, so it would be nice to have some solid dope by then! Maybe I'll see you out there!

 

[Lowlight]

Just how you're phrasing it I would say the problem starts with your environmental data,

if you are shooting CRC or up at Pawnee the temp for that DA is wrong and you're mixing values. I don't know where you got the atmospheric data, but it doesn't read like a kestrel gave it too.

I would bet your environmental data is all wrong, probably doubling it. DA should be used for field targets, not computers. It's a single solution to help explain where the bullet "thinks" it is flying. Not to be confused with actual data being used to produce a real solution. I never recommend using DA with a computer because people input the values incorrectly. It's a minute of man field solution best used inside 800m.

Steel is also a bad way to confirm without a watermark or with a smaller target to verify. If you shoot CRC confirm your data on paper to 1k, record the complete conditions for each yard line, don't shortcut it, and then you can bend the curve with your software. That includes modifying both your MV and BC as each effects different points

 

[ScottyD]

Dumb question - you said both scopes pass the tracking test with flying colors.. (Assuming you know the range)

Did you do a box test for tracking or a true calibration test like the TALL TARGET TEST? They a completely different

Hi Diver160651,

I did do a box test on the SWFA when I first got it. I recall going 2 or 3 mils up, right, down, and back left... No issues there. Then recently I put targets exactly 36" above each other at 100yds, and dialed up 10mils using the low target for POA. Both scopes drilled the upper bull with 10mils dialed on. At matches 1 month apart, both scopes have hit that 1150yd target with exactly 10.2 dialed on (while mounted on my 6.5cm, and same temp and DA), and the swfa now sits on my .223 and is tracking fine out to 600 so far... Plus I let my buddy shoot my gun at 1150yds to rule me out as the shooter, and he was on with 10.2 as well. I figured all that was enough to rule out any tracking issues. Should I still be looking more closely at that, or doing another test? Thanks for the help.

 

[ScottyD]

Just how you're phrasing it I would say the problem starts with your environmental data,

if you are shooting CRC or up at Pawnee the temp for that DA is wrong and you're mixing values. I don't know where you got the atmospheric data, but it doesn't read like a kestrel gave it too.

I would bet your environmental data is all wrong, probably doubling it. DA should be used for field targets, not computers. It's a single solution to help explain where the bullet "thinks" it is flying. Not to be confused with actual data being used to produce a real solution. I never recommend using DA with a computer because people input the values incorrectly. It's a minute of man field solution best used inside 800m.

Steel is also a bad way to confirm without a watermark or with a smaller target to verify. If you shoot CRC confirm your data on paper to 1k, record the complete conditions for each yard line, don't shortcut it, and then you can bend the curve with your software. That includes modifying both your MV and BC as each effects different points

Thanks for the input, Lowlight. My environmental data could very well be an issue because I admit this stuff confuses the hell out of me. Stuff like the differences between station pressure vs. absolute pressure and when I should use which one seems to be too much for my thick skull. I thought going with a DA reading off a Kestrel would simplify all this for me. My 550yd data is from CRC last week -the Kestrel gave me a DA reading of 6600 that day (I'm seeing that 550yds is so short that a huge DA swing shouldn't affect my POI: 2.8mils is my spot at 550 out at CRC when its 40-70F. The high power range was packed that day). The other info is from the T3 match yesterday: Kestrel telling me 6500 DA at 8:30am for site-in and an even 7000 DA by noon when I was facing that steel at 1150yds. I'm all ears if you're willing to explain in more detail where I'm going wrong here. If you're also willing to explain this statement a little deeper: "DA should be used for field targets, not computers" I would also greatly appreciate it. But the chart I posted is a pile of constants used to generate dope cards at different DA's - according to that one web article in the link. Using a constant of 59F and 0 Humidity you shift the pressure around to print out cards for every 1k worth of DA... That's how I understood it anyway... If I'm wrong there, please explain!

But I hear what you're saying that I may be going about this from the wrong direction. I will go to CRC as soon as the snow clears and do as you suggest out to 1k. My previous notes have me at ~8.1-8.4 on 1050yd steel at CRC depending on temps...

I used to use Ballistic AE on my phone with a velocity of 2800. I would pull "current atmospherics" and it usually worked for me at Raton out to 875yds and "sometimes" at CRC on steel at 1050yds (that berm where we can set steel is ~45yds back from the target bunker, right?). But I'd go to Pawnee or T3 and my AE dope would be a mess. So I said forget the phone, I'm gonna go with DA and JBM... And here I am...

I hear what you're saying about steel and watermarks. I was thinking fresh paint was enough to show me if my POI was centered or not. I admit I have no idea where on the plate I'm hitting at 1150... But I had fresh paint at T3 to confirm 700 and 800yd POI as well as the 550 at CRC... So I was feeling pretty good about those... I'll see if I can talk a buddy into working the pit for me so I can shoot some paper out there...

 

[Lowlight]

Ya, you're using bad data, I put that steel out there are T3 and it's not exactly 1150, you're using rounded UKD numbers that aren't correct. Using a 1150 is not exactly right, especially when you consider you don't know where you are hitting. Like 1050 at CRC ? Steel on the back berm is not exactly 1050 that I recall, it was like 1035 or something, but I could be recalling it wrong, however those numbers are too exact to be correct. This is why, if you are using CRC use the paper and know how centered you are at the given distances instead of guessing on the distances.

Your reference barometric pressure needs to be 29.92 in the altitude screen and the reference altitude needs to be set to 0 in the Baro screen.

DA in a ballistic computer especially the ones you're using was an after thought, not the proper way to do it, its rounding thing. Computers want the exact data to be perfect and when you go out farther with bad (read, imperfect data) it's gonna vary more. Use the actual data, Station Pressure, (No altitude) and the temp, set the humidity, even here in CO putting it at 50% is better than having it at 0, it's not much but it's enough to help compound your error. Temperature is one of the biggest factors, not just with the powder, but with the flight of the bullet. If you wing the temp you're gonna have a problem. You're compounding errors and wondering why it doesn't match up. A little here, little there it all adds up.

 

[damoncali]

A little clarity on atmospherics:

What the bullet cares about is air density. Period. But you can't measure air density directly - you have to calculate it based on the physical conditions you can measure. To do that, you need temperature, pressure and humidity.

Humidity is easy and doesn't matter very much. Leave it at 50% and you're pretty much set. If you're anal, you can put it at 0 in the desert and 100 in the jungle, or just guess.

Temperature should be obvious. Use a thermometer.

Pressure is where people get confused. This is the weather man's fault. They like to "correct" the real atmospheric pressure to what it would be at sea level. While this may make their lives easier, it's useless for shooters unless you happen to be at sea level. What you really want is the actual, physical air pressure measured at the shooting point. You can use an altimeter, kestrel, or even some range finders (My Leica will do this) to measure it. Physicists call this "absolute pressure". Weather men call it "station pressure".

You can forget about density altitude. You can forget about actual altitude. Everything (really, everything!) you need is in those three numbers, and one of them doesn't really matter (humidity).

 

[ScottyD]

Thanks a ton to all of you guys. I really appreciate everybody's time invested in this thread. I keep reading and re-reading and all this info is slowly sinking in. I see now you're all saying pretty much the same thing: I'm too sloppy with my inputs. I'm gonna start over from square one. I always thought + or - 10yds was "close enough" -I see now I need to let that idea go, and really tighten up when I collect my data. I'll try letting go of the DA concept and go with Temp and Pressure while leaving Humidity at 50%.

Thanks Frank for convincing me my distances are off -which shows me that, of course, Bryan was spot on from the beginning.

Thanks damoncali for the clarification on atmospherics. That helps a bunch! I thought DA was temp and pressure all wrapped up in one number? But you guys are saying its too sloppy and rounded to be precise at longer ranges? I see now, "corrected pressure" is the one that confuses me. "Absolute" and "Station" pressure are the same, and they are what I need to pay attention to. Just to be absolutely clear: this is the "Baro" inHg reading my Kestrel will give me on the spot at the range, right? So I'm sitting at my house at ~8200ft right now. My Kestrel is giving me an altitude 8275 and it says Ref 30.01 inHg. Does that Ref mean anything? I go to my Baro screen and it gives me 22.07inHg and says Ref 9ft -is that "Ref" anything I have to worry about? Once I have solid drop or velocity data, that 22.07 inHg, current temp, and 50% H is all I need to get my ballistic calculations rolling?

So now my goal is to get solid tracking data out to 1k, take it back to JBM, and print up a bunch of dope cards for the various conditions I'll be seeing this summer. I'll be shooting from ~4000ft to ~7000ft with temps ranging from 50F to 100F. Is there an easy way to anticipate the spread of possible pressures I'll see this summer? It was really easy to wrap my head around this using DA thanks to this:

http://demigodllc.com/icao.pdf

 

[colson]

damoncali called it: it's all about pressure and temperature. My Casio does both. You're going to see a huge spread in pressure if you are changing altitudes. I've even recorded pressure changes of one inch at my home depending on the weather, which is going to matter at longer ranges.

 

[redd0311]

Tag

 

[damoncali]

Do I have to set the Kestrel to anything different to get station pressure?

I do not own a Kestrel but my partner does and I'd like to move off of using barometric pressure provided via GPS.

I don't own one either, so someone else should chime in. But I believe there is a setting where you tell it what reference altitude you're at. If you set that at zero, you get station pressure since there is no altitude to correct for. I'm at a little over 1,000 feet, so the pressure is usually 28.5-29.0 inHg for me. If you're higher, it will be less.

Use this chart to sanity check the number you're getting out of the instrument: Sable Systems

 

[sinister]

Garbage in - garbage out...

If you have the correct tools on-site you can calculate what you need for a first shot on-target hit within a minute of angle -- that's the science part and is routinely done, day-in, day-out, by artillery and mortarmen, aircraft pilots, and others who deal with altitude and pressure (i.e., respiration and breathing specialists in hospitals). Horizontal value winds are the art in the ballistic equation.

As mentioned above you must know the difference between uncorrected (absolute) and corrected (station) pressure.

A Kestrel will work for pressure and temps. Temperature will affect your velocity, while density altitude affects bullet trajectory due to drag.

Ballistically your calcs will affect your elevation turret setting.

Real-world example: if you plug in corrected (vice absolute or uncorrected) barometric pressure into an Irvin free-fall parachuting automatic opener computer math equation at Fort Bragg, North Carolina, for a night free fall combat equipment jump at Fort Collins, Colorado, you have a recipe for catastrophe -- the opener will be set to activate 1500 feet below actual target ground level.

Following the example, for a rifle you'd be cranking elevation into your turret for a shot 1500 feet lower in density altitude than what you're aiming at.

Using data off a Kestrel and plugging into FDAC cards or a ballistic whiz-wheel you can get your turret setting without referring to other required electronic devices (like a phone, laptop, or tablet that has to be linked to an outside internet source). It's how it was done in the old (analog) days with a meteorological message or field weather station.

"Truing" your data is the ideal as your data correlates for conditions at the time in that place -- but you may not have the opportunity to true as conditions change. Artillery and mortars don't fire a round at their marked center-of-sector every day or every few hours as temperatures change.

In simple highpower rifle terms that's why traditional NRA rifle matches give all shooters two "Sighter" shots to true data before shots count for score.

 

[damoncali]

Thanks damoncali for the clarification on atmospherics. That helps a bunch! I thought DA was temp and pressure all wrapped up in one number? But you guys are saying its too sloppy and rounded to be precise at longer ranges? I see now, "corrected pressure" is the one that confuses me. "Absolute" and "Station" pressure are the same, and they are what I need to pay attention to. Just to be absolutely clear: this is the "Baro" inHg reading my Kestrel will give me on the spot at the range, right? So I'm sitting at my house at ~8200ft right now. My Kestrel is giving me an altitude 8275 and it says Ref 30.01 inHg. Does that Ref mean anything? I go to my Baro screen and it gives me 22.07inHg and says Ref 9ft -is that "Ref" anything I have to worry about? Once I have solid drop or velocity data, that 22.07 inHg, current temp, and 50% H is all I need to get my ballistic calculations rolling?

http://demigodllc.com/icao.pdf

I don't own a Kestrel so take this with a grain of salt. My guess is that the "9 ft" is that your reference altitude is 9 ft. It should be zero if I understand the way the Kestrel works, but 9 feet isn't going to jack anything up. At 8200 feet, 22 inHg sounds about right. But ask someone who is familiar with a kestrel in detail, which I am not.

 

[StampCreek]

Denisty altitude. Airplane stuff 101.

Density altitude is standard altitude corrected for non-standard pressure and temperature. What is standard? Sea level, 29.92"Hg, 15 degrees C (59*F)

Pressure drops 1" per thousand feet, temp 2*C per thousand feet. Where you are at at 8000' the standard pressure is 21.92", standard temp would be -1*C. If you have those conditions then your denisty altitude would be 8000 feet.

The Kestrel is directly reading air pressure, not getting a report from some weather station. To figure denisty altitude you still need to correct for that absolute pressure being non-standard. (to be fair you can figure denisty altitude by correcting off 29.92 or the standard absolute pressure. Both corrections get you the same info)

At 8200' with an altimeter of 30.01" you're pressure altitude is 8110'. Now we correct that for non-standard temp to get denisty altitude. Anything warmer than -1*C is going to raise that DA.

Yes, you can have denisty altitude be lower than where you are, high pressure and cold temps and at 8200' you could have a DA of 3000'. Bullet isn't gonna fly as well.

In the mountains you will see very high DAs. Remember, at 8200 feet the standard temp is -1*C. Even in July. You do still get 24 degree days, 28 degree days. DA is going to be super high.

 

[LawnMM]

I will throw this out there also, you should get a good muzzle velocity. You sound like you are working without a chronograph. If that's the case, just loose sd/es numbers can screw you at 1150+ yards.

II'm going to be at CRC next week getting a few last minute things ready for the Hide Cup if you want to use my magnetospeed. There's another guy that might take me up on that as well.

 

[StampCreek]

Check.



At 8275 feet MSL 30.01 inches of Mercury is your corrected barometric pressure or altimeter setting in aviator terms (if you were an airfield) -- so that his altimeter reads zero as his wheels touch down (not necessarily zero at the airfield he took off from if he left an airport at sea level).

Your uncorrected or absolute pressure is 22.07 inches of Mercury.

Your basic thermometer temperature will give you an idea how much your muzzle velocity might vary as your powder burns slower or faster.

Follow the prompts on JBM and make sure you click the boxes for corrected or uncorrected pressure (be consistent as to which one you're using). You don't necessarily want standard conditions at true altitude, and you have to choose whether you're plugging in corrected or absolute pressure. The difference can be as much as 300-400 Meters calculated trans-sonic range depending on the bullet you're using (with wildly varying elevation settings).

Won't read zero, will read field elevation. In the US we do QNH, not QFE, so we're at field elevation on takeoff and landing, not zero (unless you're actually AT sea level). Even using QFE (setting altimeter to zero on takeoff) it won't be zero when we land at a different airport with a different elevation. Set it to zero in Denver and go to Telluride and it will read 4000' on landing (KTEX is about 4k higher than Denver). Using QNH and altimeter settings my altimeter will read 5200 in Denver on takeoff and 9000 on landing in Telluride. Really close to field elevation. That's why we use these sea level corrected altimeters, keeps everyone close to field elevation and everyone on the same page (same altitudes) and from running into each other.

Above 18,000 feet we all use 29.92 on the altimeter. Most all traffic up there is fast moving jet traffic and we can't be resetting out altimeter every 30 seconds. Have someone screw it could and it gets noisy when metal hits metal. So, standard up there so EVERYONE in the whole country up there uses the same setting and maintains the same altitudes regardless of where they fly.

 

[Lowlight]

You're making it harder than it needs to be, reset the kestrel and drive on.

If your adjusted your kestrel settings for your location, you're wrong, it's that easy.

 

[damoncali]

Altitude is totally irrelevant. What you want is physical, absolute air pressure. Just measure the pressure and enter it into your ballistics calculator. Measure the temperature and enter it. Measure (or guess at) humidity, enter it. You're done. At no point does altitude come into the equations used by the calculator.

Unfortunately, calculators have made this more confusing than it needs to be by adding inputs for altitude, density altitude, and such. They are just alternative ways at getting at pressure, and are only useful if you can't measure the pressure directly. The tools to measure pressure are not that expensive. If you can't afford a Kestrel, get a simple mechanical altimeter for $50.

Temperature. Pressure. Humidity. That is all you need. Leave altitude to the pilots and meteorologists.

 

[steve123]

Hey Scott,

C'mon man just aim higher, what's your problem? Just kidding, I've been in those shoes before. Piss's a guy off for sure.

Usually when I have stuff like this happen there is one problem or a combination of problems happening at the same time.

For nearly two years I had a random and sporadic POI shift problem causing usually .2-.3 mils shift in any direction. It started out barely perceptible and got worse as time passed. Also I was using a chrony which gave inconsistent readings as well as false readings.

I got a Oehler which verified the chrono problem and it got my dope lining up for the most part, that and using Litz BC's.

The POI shift was from a poorly made/ uneven and partially epoxied recoil lug which caused the barrel to loosen up over time. It wasn't til I got my own action wrench and barrel vise which enabled me to check and find out what the problem was myself. A few years ago at a big match on the first stage I placed dead last, it was a easy stage too, I literally could not hit a 4" plate at 255Y off the bipod with six rounds. The next stage the rifle was fine and close enough (although I had some small shifts later during the match), for the rest of the match to claw my way up to 15th. As soon as I got home I ordered those barrel tools mentioned.

Anyway, that dope (actual come ups) does not make sense. I input your data and played with it on SHOOTER and the 1150Y target is 1.2 mils off showing 9 mils correction. 800Y is showing 5.1 and 700Y is 4.1, 550 is on at 2.8. The program is showing 1235Y for 10.2 mils correction. I know you've done the same but others are reading this thread so the info is for them.

I would find someone with a Vectronics RF to confirm distance at the 1150Y. If it's a big plate maybe you are hitting at the top which would help explain things some. Also I would double check the 100Y zero after each distance is shot to check for POI shifts.

Checking to make sure parallax is dialed out right?

Just the kind of hassle you need right now, huh? I hope you figure all this out before the cup man!

 

[SAPenguin]

Yo Scott! I'll be your pitt-monkey this weekend if you wanna go to CRC

 

[oinco]

ScottyD,

I see your pain here...the last two times we shot together I collected pressure/temp/humidity- and when I input your general parameters using those environmental numbers- I can only come kind of close (+/- .15mil)to your "confirmed" DOPE if I fudge a LOT of things(scope height/speed/zero height)- and not even close to your 900yd+ numbers...

My DOPE using the same environmentals and known distances (+/- 1yd) that we were both shooting at- matches out to 1540yds+/- my shooting inadequacies.

I very much question your 10.2mil/1150 recording- try using JBM's inch unit as column 1 in the trajectory calculator and see how far that is off....- regardless of sliding your MV up/down by a large swing?

I watched you do a box test-and the struggles you had at the range/match in matching up numbers....it makes me wonder about an issue(s) similar to what Steve123 described?

I'd burn all the DOPE you have (see what I did there)- start from zero- assume nothing- (just what you want to do as the clock is ticking on the SHC !) If it doesn't step into line- you are welcome to shoot one of my rifles- I'd "probably" provide you with pretty good DOPE. :<)

 

[delfuego]

After ScottyD got his dope squared at Raton, he proceeded to crush the last 4-5 stages cleaning a few. I would guess the rifle is OK and the DOPE was wrong. I am curious to see the solution too, My dope is spot on from 400-800y but off under 300y.

 

[ScottyD]

I will throw this out there also, you should get a good muzzle velocity. You sound like you are working without a chronograph. If that's the case, just loose sd/es numbers can screw you at 1150+ yards.

II'm going to be at CRC next week getting a few last minute things ready for the Hide Cup if you want to use my magnetospeed. There's another guy that might take me up on that as well.

Hi LawnMM!

I would very much like to take you up on that offer. Thank you! You should have a PM incoming to talk more about that!

 

[ScottyD]

OK, so check this out: KevinU was kind enough to talk me through a few things over the phone this afternoon, and suddenly JBM started getting really close to what I'm seeing.

The elevation of the T3 ranch (location of this year's cup! -and where most of my data is coming from) is ~4600ft, and the temp that day was ~65F. When I go to JBM and plug in 4600 for elevation and 65 for temp, with a 50% H, ***AND**** leave pressure at the default of 29.92, my numbers start looking real good with a velocity of 2875fps. This gives me 2.9mil @550yds (only .1 off my real world data), 4.4mil for 700yds (perfect match to my data), and 10.1mil @ 1150yds (.1 off my data)... This looks very promising -especially with some fine tuning, IMO...

The big QUESTION: Is this random and lucky? Or is it a valid solution to simply leave the pressure at the default 29.92 and just input altitude and temp in JBM? Will I run into problems with this later? You guys have been making my head spin with all your knowledge, and all the different ways to do this stuff. Please tell me this is also a valid solution!

 

[damoncali]

OK, so check this out: KevinU was kind enough to talk me through a few things over the phone this afternoon, and suddenly JBM started getting really close to what I'm seeing.

The elevation of the T3 ranch (location of this year's cup! -and where most of my data is coming from) is ~4600ft, and the temp that day was ~65F. When I go to JBM and plug in 4600 for elevation and 65 for temp, with a 50% H, ***AND**** leave pressure at the default of 29.92, my numbers start looking real good with a velocity of 2875fps. This gives me 2.9mil @550yds (only .1 off my real world data), 4.4mil for 700yds (perfect match to my data), and 10.1mil @ 1150yds (.1 off my data)... This looks very promising -especially with some fine tuning, IMO...

The big QUESTION: Is this random and lucky? Or is it a valid solution to simply leave the pressure at the default 29.92 and just input altitude and temp in JBM? Will I run into problems with this later? You guys have been making my head spin with all your knowledge, and all the different ways to do this stuff. Please tell me this is also a valid solution!

Leaving the pressure at 29.92 just means "use the standard pressure at the altitude I plugged in". 29.92 is the "corrected" or "weather man" pressure, NOT the absolute pressure. This will usually get you pretty darn close. What you've done is to use JBM's built in feature that estimates the absolute pressure from the altitude and corrected pressure. It's a little less precise than entering pressure directly, but obviously in this case, it will do.

Better yet is to measure the pressure on site when you're recording your data so you know exactly what the pressure is - altitude is a bit of a guess, and hte assumption that it's "standard pressure" is not always quite right.

 

[Kiwigrunt]

Fantastic. I have struggled with this for a while. I use the simplified JBM calcs.

So just to be absolutely utterly totally unconditionally indisputably unambiguously sure:

If I fill in the 'default' pressure of 29.92, and the altitude, I should tick the 'std atmosphere at altitude' box.

Whereas, if I fill in the measured pressure, I should tick the 'pressure is corrected' box. Should I then leave the altitude box clear, or still fill in the altitude?

 

[ScottyD]

Leaving the pressure at 29.92 just means "use the standard pressure at the altitude I plugged in". 29.92 is the "corrected" or "weather man" pressure, NOT the absolute pressure. This will usually get you pretty darn close. What you've done is to use JBM's built in feature that estimates the absolute pressure from the altitude and corrected pressure. It's a little less precise than entering pressure directly, but obviously in this case, it will do.

Better yet is to measure the pressure on site when you're recording your data so you know exactly what the pressure is - altitude is a bit of a guess, and hte assumption that it's "standard pressure" is not always quite right.

Ah, I see. Thanks again for another excellent explanation. I also put the same numbers into ballistic AE on my phone, and DID NOT get the same results. Perhaps AE does not have the same built in feature that estimates absolute pressure. Or perhaps I missed some seemingly random and yet very important setting button somewhere...

If you say a straight up on-site absolute pressure taken from my Kestrel will be more accurate, then I will give it a try. The big question now is: do I also plug in what my Kestrel tells me for altitude? Or Do I leave altitude at zero when using my on site pressure measurement (Talking about JBM specifically here)?

I've been watching every how-to video regarding JBM and AE that I can find, and it seems they all quickly brush over the atmospheric entries. Its been hard for me to dig up clear answers... Or maybe I'm just dumb... What I need is "An Idiots Guide to Atmospheric Entries" for your ballistic calculator. Haha... Seems like there is A LOT of room for us newbies to drop the ball in this department!

 

[ScottyD]

Hey Scott,

C'mon man just aim higher, what's your problem?

Ha! Hey Steve! Funny you should mention that! -That's my solution for my pistol problems lately. People tell me I'm anticipating recoil and have a horrendous flinch or something. Lately I've been getting some outstanding groups in the 2x4 target stand just below the plates I'm aiming at! haha! Ad that to the list of things I need to work on during my next range trip!

But thanks for the suggestions. If I compile a list of all the possible sources of my long range issues mentioned in this thread, it covers just about every possible component in the system, now that you've added parallax to the list! Its amazing anyone ever hits anything with all the stuff that can go wrong! haha... But seriously, it looks like there might be light at the end of the tunnel here finally. Showing up at the cup with an accurate dope card sure would be nice! Any chance you're going to make it up for the cup?

 

[ScottyD]

ScottyD,

I see your pain here...the last two times we shot together I collected pressure/temp/humidity- and when I input your general parameters using those environmental numbers- I can only come kind of close (+/- .15mil)to your "confirmed" DOPE if I fudge a LOT of things(scope height/speed/zero height)- and not even close to your 900yd+ numbers...

My DOPE using the same environmentals and known distances (+/- 1yd) that we were both shooting at- matches out to 1540yds+/- my shooting inadequacies.

I very much question your 10.2mil/1150 recording- try using JBM's inch unit as column 1 in the trajectory calculator and see how far that is off....- regardless of sliding your MV up/down by a large swing?

I watched you do a box test-and the struggles you had at the range/match in matching up numbers....it makes me wonder about an issue(s) similar to what Steve123 described?

I'd burn all the DOPE you have (see what I did there)- start from zero- assume nothing- (just what you want to do as the clock is ticking on the SHC !) If it doesn't step into line- you are welcome to shoot one of my rifles- I'd "probably" provide you with pretty good DOPE. :<)

Cheers Mr. O! Burning all my dope should help me with matches here in CO, but will still get me in trouble down at Raton, NM and up in Wheatland WY, right? haha...

Looks like I'll be heading back to the range soon. Let me know if you're interested and have any free time!

 

[damoncali]

Fantastic. I have struggled with this for a while. I use the simplified JBM calcs.

So just to be absolutely utterly totally unconditionally indisputably unambiguously sure:

If I fill in the 'default' pressure of 29.92, and the altitude, I should tick the 'std atmosphere at altitude' box.

Whereas, if I fill in the measured pressure, I should tick the 'pressure is corrected' box. Should I then leave the altitude box clear, or still fill in the altitude?

Not quite. These are slightly different options.

"pressure is corrected" means "I used weatherman pressure, not absolute pressure". You will also need to input an altitude to make this make sense (corrected from what?).

"std atmosphere at altitude" means, "ignore everything I put in except altitude, and look up the standard pressure/temperature/humidity from a magic table". This is the least accurate option.

Note that in both cases, you are are introducing more uncertainties into the system, and that's only a good idea if you haven't got a clue what to put in. JBM will do a decent job at getting a usable number. The first case, you are almost certainly not inputting pressure from your location. If you had a good measurement where you are, you'd use absolute pressure. So there is error there. In the second case, you can't even be bothered to enter a temperature. In both cases, there is uncertainty in your altitude to add to the mix.

The preferable (and easier to understand, at least to me) is to enter absolute ("non-corrected", or "station") pressure, temp, and humidity. (Uncheck both boxes). And just forget about altitude altogether. This falls apart usually because people lack pressure data and don't know where to get it (or are confused by it). But getting it isn't as hard as people think - a cheap sports altimeter (about $50) usually has a inHg scale in addition to the altitude scale. A lot of fancy sports watches have built in barometers. A properly set up Kestrel will tell you.

It's confusing stuff, and very hard to write a piece of software that makes it less so (I've tried).

 

[damoncali]

Ah, I see. Thanks again for another excellent explanation. I also put the same numbers into ballistic AE on my phone, and DID NOT get the same results. Perhaps AE does not have the same built in feature that estimates absolute pressure. Or perhaps I missed some seemingly random and yet very important setting button somewhere...

If you say a straight up on-site absolute pressure taken from my Kestrel will be more accurate, then I will give it a try. The big question now is: do I also plug in what my Kestrel tells me for altitude? Or Do I leave altitude at zero when using my on site pressure measurement (Talking about JBM specifically here)?

I've been watching every how-to video regarding JBM and AE that I can find, and it seems they all quickly brush over the atmospheric entries. Its been hard for me to dig up clear answers... Or maybe I'm just dumb... What I need is "An Idiots Guide to Atmospheric Entries" for your ballistic calculator. Haha... Seems like there is A LOT of room for us newbies to drop the ball in this department!

If you plug in absolute pressure, you do not need altitude at all. Altitude is used as a way of estimating absolute pressure because most people are more likely to know the altitude with more certainty than they do the absolute pressure. I believe you leave the JBM altitude blank and make sure you've unchecked the "pressure is corrected" box (I assume that this box just ignores whatever you put in the altitude anyhow since it won't need it).

When I get a moment, perahps I'll write that guide. There seems to be a lot of interest/confusion over this, and I bet people checking the wrong box makes for a lot of error/frustration, especially when the differences aren't that large. For me, at 1000 feet, the results look about right, but they're a little off if I use sea level atmos. That might lead me to think my chronograph is junk or that calculators just don't work.

 

[sinister]

Conversely, if you have your map handy or did a Google Earth computer recce before going out to your favorite or habitual shooting spot you'll know range elevation (off contour lines and data) and you can get a general average temperature (for the day) off weather underground or weather.com. You should know or have a good estimate on your velocity within 50-100 fps. This will allow you to do a printout the night before or just before driving out without having to buy an expensive electronics package.

If you're not intending to shoot a hostile or take an animal (either on your first and only shot) then you can adjust your data.

 

[ScottyD]

If you plug in absolute pressure, you do not need altitude at all. Altitude is used as a way of estimating absolute pressure because most people are more likely to know the altitude with more certainty than they do the absolute pressure. I believe you leave the JBM altitude blank and make sure you've unchecked the "pressure is corrected" box (I assume that this box just ignores whatever you put in the altitude anyhow since it won't need it).

When I get a moment, perahps I'll write that guide. There seems to be a lot of interest/confusion over this, and I bet people checking the wrong box makes for a lot of error/frustration, especially when the differences aren't that large. For me, at 1000 feet, the results look about right, but they're a little off if I use sea level atmos. That might lead me to think my chronograph is junk or that calculators just don't work.

You are THE MAN damoncali! Much appreciated! Final answer (for JBM): leave both of the little option boxes un-checked, leave altitude at zero, put in temp, 50% H, and your own on-site pressure measurement. Got it!

More questions: Say I want to get a ballpark estimate on what the pressure is going to be so I can show up at a match with a selection of pre-made dope cards at the ready. For example, the cup is being held very close to the town of Weldona, CO. If I go here:

Weldona, Colorado (80653) Conditions & Forecast | Weather Underground

One of the first things it lists is a pressure of 30.43 inHg. Is this corrected pressure (if so, is there another place I can get the absolute measurement I'm after)? Or is this an absolute that shouldn't be too far off from what I might see when I show up with my Kestrel? Also, how much of a pressure shift is going to be significant to us shooters? If I made cards for every .5 of inHg (30.5, 30.0, 29.5, 29.0, 28.5....) for example(with a range of temps to go along with each pressure) would I be covered? Would I want to go any looser or tighter with my pressure spread? Am I on the right track here? My goal: I want to roll in to a match with a stack of cards, pull out my Kestrel to check pressure and Temp, then select the card that is the closest match, and then go center-punch that steel all day long! haha!

EDIT: Looking at your Sable Systems table, I see pressures for 4500ft should be in area of ~24-27inHG... So that 30.43 from underground must be corrected, right? -And therefore the 30.43 number is no good to me... Would a range of cards from ~24-27 inHG have me covered?

 

[damoncali]

You are THE MAN damoncali! Much appreciated! Final answer (for JBM): leave both of the little option boxes un-checked, leave altitude at zero, put in temp, 50% H, and your own on-site pressure measurement. Got it!

More questions: Say I want to get a ballpark estimate on what the pressure is going to be so I can show up at a match with a selection of pre-made dope cards at the ready. For example, the cup is being held very close to the town of Weldona, CO. If I go here:

Weldona, Colorado (80653) Conditions & Forecast | Weather Underground

One of the first things it lists is a pressure of 30.43 inHg. Is this corrected pressure (if so, is there another place I can get the absolute measurement I'm after)? Or is this an absolute that shouldn't be too far off from what I might see when I show up with my Kestrel? Also, how much of a pressure shift is going to be significant to us shooters? If I made cards for every .5 of inHg (30.5, 30.0, 29.5, 29.0, 28.5....) for example(with a range of temps to go along with each pressure) would I be covered? Would I want to go any looser or tighter with my pressure spread? Am I on the right track here? My goal: I want to roll in to a match with a stack of cards, pull out my Kestrel to check pressure and Temp, then select the card that is the closest match, and then go center-punch that steel all day long! haha!

EDIT: Looking at your Sable Systems table, I see pressures for 4500ft should be in area of ~24-27inHG... So that 30.43 from underground must be corrected, right? -And therefore the 30.43 number is no good to me... Would a range of cards from ~24-27 inHG have me covered?

Yes, that 30.43 is a corrected pressure, and no good to you. UNLESS - you also enter an altitude and tell JBM that your'e using corrected pressure. But why bother. If you just want to get a ballpark, find the altitude of the location, look up the standard pressure for that altitude, and enter a reasonable temperature and humidity. It won't be perfect, but it will be close. It eliminates pressure confusion if you always use the same method. If you're on site, measure the pressure. If you're off site, look up an estimate.

Your multi-card system is certainly doable, but it's going to be a lot of cards. More like a book if you want to cover every reasonable combination. That's a ton of work if you do it manually. (This is one piece of software I've been thinking about building- a rifle specific "book" generator. I'm not sure how useful it would be, though.) I would work up a baseline for location and weather you're anticipating ahead of time and if things change dramatically, crank one out by hand using the kestrel data on the day of the shoot.

 

[colson]

Your multi-card system is certainly doable, but it's going to be a lot of cards. More like a book if you want to cover every reasonable combination. That's a ton of work if you do it manually. (This is one piece of software I've been thinking about building- a rifle specific "book" generator. I'm not sure how useful it would be, though.) I would work up a baseline for location and weather you're anticipating ahead of time and if things change dramatically, crank one out by hand using the kestrel data on the day of the shoot.

damoncali: you seem to really know this subject; could you please take a look at my thread on Firing Solution Tables and let me know what you think?

I think that my solution to the "book" or "multi-card" problem has a lot of potential. The basic premise of my tables is that there are only so many elevation firing solutions and that different barometric pressure and temperature inputs will result in those solutions. Granted, my particular example is not as precise as some would like, but that is easily adaptable. (I use 1 MOA elevation increments)

 

[high right]

Scott
I don't think we are ever going to see pressure like the ones you list here in Colorado.
When we shot Raton I looked at the absolute pressure it was 24.25 or something in the
morning.

 

[artee]

Scott, on pressure ranges consider this:
At sealevel (29.92" standard) you hardly ever see a higher pressure than 30.60 in. You Seldom see a lower pressure than 29.50 inch. When you do see a lower pressure, it's with a tornado passing over you or you're in the eye of a hurricane. The pressure readings on the surface at the eye of a hurricane are 28.something. If its REALLY STRONG, maybe, just maybe 27. something inches. It takes cutoff polar lows (like over the Midwest much of last winter) to exceed 30.40 in and raging hurricanes to dip below 29.00 inches.

SO for a HIP POCKET number, pressure is usually no more than 1/2 in ABOVE or BELOW standard.
Now, move up to a higher ELEVATION of ground. Take the 4439ft Weatherunderground has for the station elevation of your Weldona, CO. It would have a STP pressure (pressure at standard pressure and temp) or 25.43in (straigt linei interpolation from your Sable systems chart vales of 25.84" at 4000 ft and 25.37" at 4500 ft)

Your HIP POCKET numbers for Pressure at Weldona is therefore 25.43in and 24.90 to 25.90 inches covers 99.9% of any condition you'd ever see there for actual, non corrected, as read of an absolute pressure gage Pressure.

 

[earthquake]

Scott, thanks for bringing this up! I've been following this thread since day one and am in a very similar (the same?) boat as you...shooting the Cup, confusion about JBM weather inputs, missing some good load data.

Anyway, I shot last Saturday and didn't have a chrony, nor my barometer! Was doing load development (my first ever) and was trying to get DOPE on these loads. I did get some numbers, and w/o stepping on your post here, maybe this will add to the discussion?

Unknown variables: MV and pressure
I zeroed the rifle at what I thought was 100 yards, but turned out to be 93 yards as measured with an LRF

Known:
6.5 Creedmoor
140 Berger Hybrids
42.3 gr H4350
25" barrel
scope clicks are 0.1 mil

Actual elevation: 4,825 ASL (just south of Pawnee Grasslands, pretty close (15mi) from SHC)
Temperature: ~66 F

Some drops I noted:
300 yards = 1.0 mils
440 yards = 2.1 mils
521 yards = 2.5 mils
600 yards = 3.4 mils
800 yards = 5.4 mils
1,000 yards = 7.8 mils

So plugging this into JBM, I was getting 2,850 fps for my MV. That's with a pressure of 29.92 inHG (which I didn't touch). If, based on what others are saying is true, that it drops 1" per 1,000' of increased altitude, it should be ~25 inHG. Putting that in JBM I have to drop my MV to ~2,765 fps.

I have noticed that either changing MV or inHG makes a BIG difference in JBM. I also looked up these links:

Barometer Graphs

DIA pressure

...and see that they listed ~29.77 inHg for the Denver area on 5/10 (the day I was shooting just north of there).
---------------------------------------------
So here's the gist of my question, I put in JBM:

2,765 fps for MV
29.77 inHg for pressure
30% humidity
66 F temp
4,825' Altitude
checked the box "Pressure is corrected"
--------------------------------------------
IS THAT RIGHT? It matches pretty close, but is my MV really that low, or is my pressure entry off?

Or, is my mv closer to 2850 and pressure is really ~25 inHg????

sheesh! If I read the baro inHg on my wrist watch, is that actual, at my site/arm and THAT goes into my ballistics computer (iSnipe) or what?

Sorry for the long winded post, but I too am trying to get to the bottom of this.


*Edit to add:

in JBM these entries are...

2,850 fps & 29.77 = bad
2,765 fps & 29.77 = good!
2,850 fps & 25.00 = Very bad >500 yds.
2,765 fps & 25.00 = bad >600 yds.

based on info I gathered last weekend...

 

[colson]

Unknown variables: MV and pressure
I zeroed the rifle at what I thought was 100 yards, but turned out to be 93 yards as measured with an LRF

Known:
6.5 Creedmoor
140 Berger Hybrids
42.3 gr H4350
25" barrel
scope clicks are 0.1 mil

Actual elevation: 4,825 ASL (just south of Pawnee Grasslands, pretty close (15mi) from SHC)
Temperature: ~66 F

Some drops I noted:
300 yards = 1.0 mils
440 yards = 2.1 mils
521 yards = 2.5 mils
600 yards = 3.4 mils
800 yards = 5.4 mils
1,000 yards = 7.8 mils

So plugging this into JBM, I was getting 2,850 fps for my MV. That's with a pressure of 29.92 inHG (which I didn't touch). If, based on what others are saying is true, that it drops 1" per 1,000' of increased altitude, it should be ~25 inHG. Putting that in JBM I have to drop my MV to ~2,765 fps.

I have noticed that either changing MV or inHG makes a BIG difference in JBM. I also looked up these links:

Barometer Graphs

DIA pressure

...and see that they listed ~29.77 inHg for the Denver area on 5/10 (the day I was shooting just north of there).

So here's the gist of my question, I put in JBM:

2,765 fps for MV
29.77 inHg for pressure
30% humidity
66 F temp
4,825' Altitude
checked the box "Pressure is corrected"

IS THAT RIGHT? It matches pretty close, but is my MV really that low, or is my pressure entry off?

Or, is my mv closer to 2850 and pressure is really ~25 inHg????

sheesh! If I read the baro inHg on my wrist watch, is that actual, at my site/arm and THAT goes into my ballistics computer (iSnipe) or what?

Sorry for the long winded post, but I too am trying to get to the bottom of this.

29.77 sounds like a corrected pressure for your altitude, thus clicking that box is the thing to do, if you want to use corrected pressure.

My default is to always uncheck that box and enter the station pressure from my watch. If you do this then it doesn't matter what altitude you enter, 0-100000.

Remember: it's all about temp and pressure and mv. Humidity doesn't really matter until you get past 1000 or so.

 

[dentout]

tag

 

[delfuego]

Corrected pressure at DIA currenty is 24.91". This is also know as station pressure and has been "corrected" for altitude.
The pressure reading shows 30.42" not corrected for altitude.

NWS Denver-Boulder, CO

You can use either setting just make sure the box is check or un-checked accordingly.

From JBM Definitions:

Pressure
The barometric pressure. It may be corrected or uncorrected depending on the state of the "Corrected Pressure" checkbox.
Pressure is Corrected
Check this box if the pressure entered is a corrected station pressure. If it is an absolute pressure, leave this unchecked.

 

[colson]

Corrected pressure at DIA currenty is 24.91". This is also know as station pressure and has been "corrected" for altitude.
The pressure reading shows 30.42" not corrected for altitude.

NWS Denver-Boulder, CO

You can use either setting just make sure the box is check or un-checked accordingly.

From JBM Definitions:

Pressure
The barometric pressure. It may be corrected or uncorrected depending on the state of the "Corrected Pressure" checkbox.
Pressure is Corrected
Check this box if the pressure entered is a corrected station pressure. If it is an absolute pressure, leave this unchecked.

Actually, "Station Pressure" is the true, uncorrected pressure at a specific place.

 

[steve123]

Ha! Hey Steve! Funny you should mention that! -That's my solution for my pistol problems lately. People tell me I'm anticipating recoil and have a horrendous flinch or something. Lately I've been getting some outstanding groups in the 2x4 target stand just below the plates I'm aiming at! haha! Ad that to the list of things I need to work on during my next range trip!

But thanks for the suggestions. If I compile a list of all the possible sources of my long range issues mentioned in this thread, it covers just about every possible component in the system, now that you've added parallax to the list! Its amazing anyone ever hits anything with all the stuff that can go wrong! haha... But seriously, it looks like there might be light at the end of the tunnel here finally. Showing up at the cup with an accurate dope card sure would be nice! Any chance you're going to make it up for the cup?

My wife and I have our 2 week vacation planned right then so it didn't work out to come.

I'm too used to thinking with DA from the Kestrel now! I haven't had any problems using it and it is easy. I've also just been using my smart phone to get dope and then writing it down for the stage. Keep in mind that out to 400Y you can put in a estimated middle of the day DA and it won't change your dope out to that distance, this is for 1000' variance of total DA from morning to afternoon. It won't change your dope but 1 click, if that, out to 700Y or so using the same 1000' change. 1 click is a little over 2" at 700Y so it's more likely that a miss at a 1.5 moa steel will be from wind or a unsteady position.

Honestly I've only been worried about getting the DA right then for farther targets lately vs what I already mentioned about estimating for mid day.

Couple tips... Take the time to build your position then concentrate on hitting every target vs trying to beat the clock and ending up missing a bunch. Try-try-try to eliminate mistakes! Mistakes like not having your mag loaded all the way or forgetting to dial, or not fully understanding the stage/ because you might be called up first. Avoiding mistakes alone can net you a visit to the table with the better prizes!

With your pistol watch that front sight, press strait back on the trigger and follow through, exactly like if you were shooting a AG. Never attempt to shoot faster than your ability level!

Good luck to you Scott!

 

[Lowlight]

I did a short video showing the two methods to use, I didn't use JBM, but really just leave that stuff unchecked.

it's much simpler than you'll all making it, and with two program and both methods the results are similar.

Sure you still have to true stuff, MV, BC, etc, the program cannot account for all the variables, including how you release the shot, but it should be within a minute, especially with some pretty standard bullets.

There is a ton of data out there, don't get wrapped around the axle.

 

[17874]

I've been struggling with this for a while now. I've been through 2 iPhone apps, loads of JBM print outs, stacks of chrono numbers with a cheap F1, and two scopes (swfa 5-20, and now a kahles 6-24) that have both passed tracking testes with flying colors... I'm shooting 140 A-max in a 25" 6.5cm with 42.4g of H4350. 1.8" scope height. I believe my velocity to be ~2800 fps, but I don't know what to think at this point... My 100yd zero is as good as its going to get...

7000 DA measured with a Kestrel, I go shoot 550yds and get impacts with perfect elevation with 2.8 mils. (JBM gives me a velocity of 2875fps for this)

7000 DA 700yds and I'm centered up at 4.4 mils (JBM tells me my velocity is 2800)

7000 DA 800yds and I'm getting hits with 5.4 mils (JBM tells me my velocity is 2800)

7000 DA 1150yds and I'm confirmed on steel with 10.2 mils (JBM puts me at a velocity of 2725 for this!)

I plug my info into JBM, using the Litz BC for my A-max's, and using a temp of 59 F, humidity 0, and a pressure of 24.25 to generate a 7000 DA dope card -Those numbers come straight from here:

Making Ballistic Cards Using Density Altitude

It says:

"To keep this simple, here are combinations of temperature and pressure that will give you DA steps from -4000 feet to 11,000 feet which you can put directly into your ballistic calculator. Leave the humidity set to zero. If you need other increments or steps outside this range, just use the online calculator.

DA.............Pressure......Temp(F.)
-4000.........29.765........0
-3000.........28.925........0
-2000.........28.106........0
-1000.........27.303........0
0................29.95.........59
1000...........29.055.......59
2000...........28.208.......59
3000...........27.382.......59
4000...........26.573.......59
5000...........25.783.......59
6000...........25.011.......59
7000...........24.257.......59
8000...........23.521.......59
9000...........22.802.......59
10000.........22.099.......59
11000.........21.414.......59


I'm desperate for a dope card that works. A JBM card with a velocity of 2875 had me tracking well to 600yds, then I lose it at 700 and beyond... A JBM card with a velocity of 2800 gets me on at 700-800 but has me missing close shots and long shots... Both 2875 and 2800fps have me missing all day long at 1000+ yds.... Pulling my hair out at this point. Got some big matches coming up and I need to get this sorted out!

Any help or suggestions would be GREATLY appreciated!

Use G1 and see how things line up. I use shooter and with solid chronograph numbers it has never been off more than .1 mil for me.