Range Report Shooter app, Why Temperature w/ Density Altitude

[Ryo]

Okay I'm no expert on Density Altitude, but isn't that calculated based on air temperature, altitude, barometric pressure, and humidity? If so, then why does the Shooter app (using Android) have Temperature right under the Density Altitude as a modifiable value if Density Altitude is calculated with temperature? Is the temperature some type of anchor in the mathematics of the calculations? I do know modifying the temperature in Shooter would effect my dope by 0.1 mils per 10F (as a estimate). I just thought this was interesting..

On a side note is it better to use Shooter with the Kestrel bluetooth to get the altitude, etc data or just keep it on density altitude? I found density altitude easily got my elevation perfect on 700 yard targets.

 

[00bullitt]

Re: Shooter app, Why Temperature w/ Density Altitude

Shooter utilizes temp when selecting DA sot hat the proper speed of sound can be calculated. Speed of sound is directly related to temperature.

Some other programs that allow a Density Altitude input do not recognize temperature and cannot calculate for speed of sound at a given temperature. Those programs will become inherently inaccurate at ranges beyond 500 yards.

 

[Ryo]

Re: Shooter app, Why Temperature w/ Density Altitude

Oh nevermind figured it out..

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Compensation for Change of Muzzle Velocity with Temperature

There are many combination of temperature and pressure that will give you the same Density Altitude - but muzzle velocity is also a function of temperature. So, using this method, you must compensate for the fact that your muzzle velocity will be slower at lower temperatures, and faster at higher temperatures. How much? That depends on the powder and primer you use. I have seen muzzle velocities which vary by as little at 0.6 feet/second per F°, and by as much at 5 feet/second per F°.

The only way to know is to test your load over a chronograph at different temperatures. Once you have done that, experiment with your ballistic calculator to see how much difference it makes. One rule of thumb is to change the DA by 500 feet for every 15 fps change in muzzle velocity. If the muzzle velocity has increased with respect to your baseline temperature, which is usually the case at a higher temperature, step up in DA. If the muzzle velocity has decreased with respect to your baseline temperature, step down in DA.

The only way to know for sure is to test the response of your load with temperature.

In this case, I have tested the load which I shoot, and I know that the change of muzzle velocity with temperature is 1 foot per second per F°. Since I am shooting at a temperature which is 15 degrees cooler than I measured my muzzle velocity at, I will follow the rule of thumb above. So, since the temperature is cooler, rather than use the previously selected 10.5 mils for a DA of 7500 feet, I will use the one for 7000 feet of 10.6 mils.

Note that the difference is not large. But if I were shooting at a temperature of 5 F°, the difference would be a lot more significant. In that case, I'd have a temperature difference of 65 degrees, and I'd probably need to use a DA step which was about 2000 - 2500 feet lower than what the Kestrel indicated. That would give me an elevation of about 10.9 or 11.0 mils on a 1000 yard shot if the Kestrel DA reading was the same. </div></div>

 

[Ryo]

Re: Shooter app, Why Temperature w/ Density Altitude

Thanks 00bullitt. Just noticed your post. That makes sense.

 

[Killswitch Engage]

Re: Shooter app, Why Temperature w/ Density Altitude

Turn on your auto atmosphere feature and it will use gps to give your current density altitude from your current location. It really works awesome. I have my kestrel to get da if I need to but since I turned.the feature on I love it. Everytime you change your Target distance it repopulates your da for updated dope.

 

[steve123]

Re: Shooter app, Why Temperature w/ Density Altitude

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Killswitch engage</div><div class="ubbcode-body">Turn on your auto atmosphere feature and it will use gps to give your current density altitude from your current location. It really works awesome. I have my kestrel to get da if I need to but since I turned.the feature on I love it. Everytime you change your Target distance it repopulates your da for updated dope. </div></div>

I have the previous shooter app for droid and have a question.

I had always assumed that the program used atmospherics info from the nearest weather station because That's what I thought I had read somewhere. I've been using DA from the Kestrel instead.

So if I turn on the auto atmosphere it'll give me the correct DA for my immediate location? How would the phone get the temp, humidity to calculate DA?

 

[Ryo]

Re: Shooter app, Why Temperature w/ Density Altitude

Thats what i would aasume that it is taking from a station, not at your position.. Should test.

 

[Killswitch Engage]

Re: Shooter app, Why Temperature w/ Density Altitude

I believe it takes the temp and shit from a close station and uses gps to get your actual asl and figures it that way. Not sure though but it is usually within a 100ft or so of my kestrel so good enough for me.

 

[sobrbiker883]

Re: Shooter app, Why Temperature w/ Density Altitude

00bullit is right on. When most programs use DA, the temp provides the mach speed for conditions.

 

[ScottyS]

Re: Shooter app, Why Temperature w/ Density Altitude

I've found that simply entering observed pressure, temperature, and humidity works wonders. The only reason to calculate DA yourself is if you are using cards and not a program at the time. Using a GPS to get altitude is still winging it. Actual air pressure is what you need.

 

[Ryo]

Re: Shooter app, Why Temperature w/ Density Altitude

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ScottyS</div><div class="ubbcode-body">I've found that simply entering observed pressure, temperature, and humidity works wonders. The only reason to calculate DA yourself is if you are using cards and not a program at the time.</div></div>

I always wondered if it was best to use my Kestrel 4500NV to send the info over via Bluetooth or just manually enter in the DA. In my TBAC class I was manually entering it in DA instead of the BT connection and it was pretty much dead on. Definitely using DA for making my cards. (don't want to depend on electronics due to Murphy's law).

 

[ScottyS]

Re: Shooter app, Why Temperature w/ Density Altitude

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Ryo</div><div class="ubbcode-body"> (don't want to depend on electronics due to Murphy's law). </div></div>

Truth.

 

[scratch]

I understand that the temperature is supposed to be used together with the velocity variation due to changes in the powder temperature.
However I am getting different trajectory solutions when I change the temperature, even though I have put in zero in velocity variation, and I am keeping my density altitude fixed.
So density altitude is fixed, muzzle velocity is fixed, and still I am getting different trajectory solutions when I change the temperature in shooter. How is this possible?

kind regards
Scratch