Jbm question

[4dds]

If you put you DA in the altitude column and check std atmosphere at altitude will it use DA or am I misunderstanding it.

 

[Jack Master]

Standard station pressure at sea level is 29.92 at 59 degrees.
For each 1000 feet of elevation gain is about -1 station pressure. (2000 ft = 27.92)
If you check the std atmosphere at altitude you'll get the standard station pressure and possibly std temp (59). This might be close to your DA but barometric pressure differences from the standard pressure and temp might need you to be at a different DA. I doknt think what you are trying to do will get you to the correct DA.

 

[4dds]

I didn't think it was working right. I have a recorded DA of -2792 at 23* 30.08 65%Rh and when I input -3000 and standard it gives me 69* 33.31 0%RH. It also creates a 2.25 MOA difference at 1000. Looks like I get to redo the DA chart once again.

 

[Deleted member 113831]

If you input temp, humidity, and station pressure with the "std pressure" box unchecked, it will use the inputs you provided, regardless of altitude.

If you provide an accurate altitude, and check the "std pressure" box, then it will give you a solution based on standard conditions at that altitude, regardless of the other inputs .

 

[Alpine 338]

 

[Matches Malone]

Making Ballistic Cards Using Density Altitude

 

[4dds]

If you input temp, humidity, and station pressure with the "std pressure" box unchecked, it will use the inputs you provided, regardless of altitude.

If you provide an accurate altitude, and check the "std pressure" box, then it will give you a solution based on standard conditions at that altitude, regardless of the other inputs .

I looked at one of their definitions by clicking the question mark and it said something about Density Altitude that had me confused. I tried to find it again and couldn’t. I since went through and looked at all previous data and came up with a general DA for 10* temp changes.
Sometimes I tend to overthink things for a little while.

 

[Alpine 338]

Why are you so worried about DA, especially if using JBM? So many people get so wrapped up around the axle about DA. Every match I see people scurrying around worried about the DA. If you're shooting at a known location, you can easily find out what the altitude is at that location. With that information, and knowing what the current temperature is, you can easily have accurate Dope cards that rely on air temperature vs DA. Remember, DA is a function of Altitude and Temperature. Many cell phones, automobile's, even watches now have a thermometer. I carry a small key fob size thermometer with me as a backup, which is accurate to within +/- 2 deg. I print out JBM based dope cards in 10-deg F increments, and with a 10-deg swing, most dope doesn't change under 600-yards.

Don't turn something so simple into a difficult process.

 

[Deleted member 113831]

Why are you so worried about DA, especially if using JBM? So many people get so wrapped up around the axle about DA. Every match I see people scurrying around worried about the DA. If you're shooting at a known location, you can easily find out what the altitude is at that location. With that information, and knowing what the current temperature is, you can easily have accurate Dope cards that rely on air temperature vs DA. Remember, DA is a function of Altitude and Temperature. Many cell phones, automobile's, even watches now have a thermometer. I carry a small key fob size thermometer with me as a backup, which is accurate to within +/- 2 deg. I print out JBM based dope cards in 10-deg F increments, and with a 10-deg swing, most dope doesn't change under 600-yards.

Don't turn something so simple into a difficult process.

^^^^^^This.

 

[Sheldon N]

If you're shooting at a known location, you can easily find out what the altitude is at that location. With that information, and knowing what the current temperature is, you can easily have accurate Dope cards that rely on air temperature vs DA.

Yep.

Every match I go to I get physical altitude off the map using this link below, then pull weather forecast data and print up manual dope cards with JBM.

Find the Elevation on a Map

Determine the elevation when a point is tapped/clicked on a map

www.daftlogic.com

I may use DA and the Kestrel for convenience, but the hard copy paper dope is always there.

 

[_Windrider_]

I looked at one of their definitions by clicking the question mark and it said something about Density Altitude that had me confused. I tried to find it again and couldn’t. I since went through and looked at all previous data and came up with a general DA for 10* temp changes.
Sometimes I tend to overthink things for a little while.

DA changes 1000 ft approx every 15 degrees F.

butblike many have said before, if you are using a calculator, don’t use DA, input the individual variables. For field expedient solutions, DA is good as long as you understand the limitations.

 

[4dds]

This is the definition that sparked the question. I was just trying to figure out what the best way to build the chart I have been working on. @Jack Master thread on all his various data book pages sparked me getting off my tail and getting a simple single chart built and while I was playing with inputs in and found the difference. I have since went back and checked a bunch of my data and compiled what I feel like is a decent dope chart. Now I just need to get them printed and laminated.