Air pressure/humidity/altitude/temperature etc

[dgcie]

Hi all...

Im shooting 223 out to about 500 yards and at the moment my only considerations before a shot are bullet drop and windage.

Like most people I suspect, Im always trying to tighten my groups and push my range out further.

Do you think it would be overkill to start keeping records of humidity/altitude/air pressure/temperature etc for 223 inside 800 yards.

I always kinda assumed that kind of meticulous attention to detail was for "real-long-range" shooting.

 

[kaspermj]

Re: Air pressure/humidity/altitude/temperature etc

Hi

In my experience within those ranges it wont make a huge difference. But it will be noticeable.
I usually don't shoot .223 but it will probably deviate more than a .308 or .338.

Long story short. It will never be overkill to track these things. You might end up seeing no impact shift what so ever. But then you will know.

Humidity is really not that important. Don't bother with it.
Altitude doesn't matter at all.
Air pressure is the important one to notice.
Air temperature is irrelevant. But your ammo temp. is important.

Things to remember could be to make sure you have a solid zero before doing this. At those ranges you are talking about the differences will probably be quite small.

Focus on ammo temperature and air pressure. Ignore everything else.

 

[dgcie]

Re: Air pressure/humidity/altitude/temperature etc

Ammo temperature? Ive never heard about that before... how do you measure/control that?

 

[Greg Langelius *]

Re: Air pressure/humidity/altitude/temperature etc

More data is not a handicap, but it has to have a useful purpose.

I would not seriously consider using the .223 for beyond 600yd. I would use the .260 Rem for out to 1000yd at least, and for the limits of my own marksmanship skills, my top choice would be the .280 Rem.

Well, ammo temp is significant, but I'd simply stick to keeping it out of the sun, and exercising caution if it becomes hot to the touch. I'd also extract and set a round aside to cool if it has been sitting in a hot chamber for some lengthy time. Basically, hot loads and hot temps will conspire to blow primers. BTDT. Yet another reason to avoid hotloading.

I have gone so far as to keep ammo in a a chilled cooler. This also has hazards, as condensation can form on the ammo once you take it out, and wet ammo can also blow primers (Heat and Steam?). BTDT too.

Greg

 

[kaspermj]

Re: Air pressure/humidity/altitude/temperature etc

You guesstimate it. In most cases it will be the same as the air.
When I pick up my ammo its from a bunker that is kept at 8'C. So I need to take that into account

If it has been lying in the sun it might be warmer.
You can be a couple of degrees off and you will still be fine. And you will eventually learn to feel with your hand, if it is 5-10-15 or 25'C

The reason it is important is that most gunpowder's burn at different rates at different temperatures.
When cold it burns slower giving you a lower muzzle velocity. Meaning you hit impact low on your target.
If its hot it will burn faster increasing your MV. making you hit high.
Some powders are unaffected by this but most are.

I think a lot of shooters has a wrong idea of temp. The bullet doesn't care about how hot the air is. Bur it cares about how dense it is. Air temp. generally changes the air pressure. And air pressure affects the bullet.
The changes in air pressure due to temp and elevation is not necessarily constant so ignoring that and just measuring AP is in my experience the way to go.

That being said. Without having tried it or doing the math. I don think you will see any shift with a .223 within 500 more than 0,1-0.2mils.

 

[sled_mack]

Re: Air pressure/humidity/altitude/temperature etc

Kaspermj - That's the first I've heard of ignoring altitude. Do you say that because knowing air pressure makes up for worrying about altitude? (Not challenging you, I'm still learning a lot about all of this myself.) Along those lines, I use Density Altitude and ignore actual altitude. But I still record pressure, temperature, and humidity.

Danny408 - Start recording all of it. What's the harm at this point, waste a little ink? Once you have all of that data, you can look back over a few seasons and decide what changes affected your shots. Personally, I record temp, humidity, pressure, and DA, wind, and sun (brightness and direction). Might be overkill, but at least I'll have that data in a year to look back on and decide what is not needed.

 

[Killer Spade 13]

Re: Air pressure/humidity/altitude/temperature etc

Get a Kestrel and use the density altitude . . . takes care of all of your concerns.

Print out a ballistics card with 0,1000,2000 and 3000 feet altitudes. Interpolate between altitudes to select your drop compensation.

 

[kaspermj]

Re: Air pressure/humidity/altitude/temperature etc

I am going to step careful now. English is not my first language

I could be wrong about this definition. But Density altitude is the altitude found from the air pressure using a standard model. Not necessarily the exact height above main sea level.
So what I am saying that I would not want to worry about knowing my actual altitude. I think most gizmos like a kestrel uses air pressure to find your altitude anyway
There is no way the altitude can affect my bullet. The altitude can affect air pressure that affects my bullet.

I track the same as you. Pressure and temperature. I don't care much about humidity. I think the impact shift is so minimal that it doesn't matter at all. If I would have to shoot out to a mile I would probably take it into account. But within 1000-1200 meters I don't care and it works fine for me.

I would kind of agree with you. Just log everything. But if the shooter has little experience doing this, it might be difficult to determine what factors are causing the impact shift. That is why I recommend ignoring some factors that I have found to be either irrelevant or of less importance.

 

[msflyer]

Re: Air pressure/humidity/altitude/temperature etc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Danny408</div><div class="ubbcode-body">Hi all...

Im shooting 223 out to about 500 yards and at the moment my only considerations before a shot are bullet drop and windage.

Like most people I suspect, Im always trying to tighten my groups and push my range out further.

Do you think it would be overkill to start keeping records of humidity/altitude/air pressure/temperature etc for 223 inside 800 yards.

I always kinda assumed that kind of meticulous attention to detail was for "real-long-range" shooting.</div></div>


If you want to pick apart how much temp/altimeter/altitude/wind changes everything, go to the JBM ballistic calculator - enter your load data - start changing these variables one at a time. A little change can make a big difference and they are cumulative.

JBM - http://www.jbmballistics.com/ballistics/calculators/calculators.shtml

 

[gstaylorg]

Re: Air pressure/humidity/altitude/temperature etc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Danny408</div><div class="ubbcode-body">Hi all...

Im shooting 223 out to about 500 yards and at the moment my only considerations before a shot are bullet drop and windage.

Like most people I suspect, Im always trying to tighten my groups and push my range out further.

Do you think it would be overkill to start keeping records of humidity/altitude/air pressure/temperature etc for 223 inside 800 yards.

<span style="color: #FF0000">I always kinda assumed that kind of meticulous attention to detail was for "real-long-range" shooting.</span> </div></div>

Meticulously record <span style="font-style: italic">everything</span>! The piece of data you didn't record will be the exact one you want to look at a month or more down the road, regardless of the range you're shooting.

 

[kraigWY]

Re: Air pressure/humidity/altitude/temperature etc

Air temps do make a differenc. I shoot 223s (Service Rifle AR) at 200,300,600 and 1000 yards.

Normally every 15 degrees in temp changes impact 1 MOA.

Alitude makes a difference, I can tell the difference shooting at Little Rock and 29 Palms. Don't let any one tell you it doesn't

Ammo temps also makes a difference. In long range we normally single loaded, keeping the ammo in the shade until its ready to be chambered.

If one really wants to check ammo temp, go to the auto parts store and buy one of those laser temp gages. Shoot the red dot at a objcet and you get a digital reading of the temp of that object.

When I put on CMG GSM or High Power Clinics I use the laser temp gage to show the temp of the chamber and how hot a round gets setting in the chamber. Remember every 15 degrees or so changed you impact 1 moa.

 

[sled_mack]

Re: Air pressure/humidity/altitude/temperature etc

Kaspermj - I understand now. There is more to Density Altitude than just pressure. I pay more attention to DA than I do to actual altitude.

 

[petesp]

Re: Air pressure/humidity/altitude/temperature etc

When you are using the Kestrel for density alt, how often does a guy need to set the reference alt for accurate field measurement?

 

[Lowlight]

Re: Air pressure/humidity/altitude/temperature etc

Don't set the reference altitude, it needs to be zero and the Baro reference needs to be 29.92

 

[ashland]

Re: Air pressure/humidity/altitude/temperature etc

Are you saying in order to get accurate DA the Baro needs to be set at 29.92 every time?

 

[RobertB]

Re: Air pressure/humidity/altitude/temperature etc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ashland</div><div class="ubbcode-body">Are you saying in order to get accurate DA the Baro needs to be set at 29.92 every time? </div></div> What is the best way to calibrate? Without buying their calibration kit.

 

[Lowlight]

Re: Air pressure/humidity/altitude/temperature etc

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: ashland</div><div class="ubbcode-body">Are you saying in order to get accurate DA the Baro needs to be set at 29.92 every time?</div></div>

No, the "reference barometric" is set to that, this way you have absolute pressure and not corrected pressure. . The "reference Altitude" is also set to 0 if you adjust it you then have corrected pressure.

Look at your Kestrel and you'll see the reference numbers which are below the readings.

 

[petesp]

Re: Air pressure/humidity/altitude/temperature etc

Thanks, appreciate the help.

 

[ashland]

Re: Air pressure/humidity/altitude/temperature etc

Got it. Thank you.

 

[RingingSteel]

Re: Air pressure/humidity/altitude/temperature etc

As far as atomspheric conditions I use the same DOPE out to 600 yards. From 600 out I do get the Kestrel out and check the DA and make adjustments from there. As far as I'm concerned using DA and a G7 BC is the only was to go at extended ranges.

 

[Rick 324]

Re: Air pressure/humidity/altitude/temperature etc

Great Topic!!! I went from shooting at 5500 ft in Abq, NM to shooting at 800 ft here in San Antonio, TX and I can say that the only change that I can find is the Air Pressure. Living that high up you are at a lower pressure due to the lesser amount of Oxygen in the air!!!

I think that most people pay attention to both Pressure and Temp only because as stated above, temp will affect the burn rate of your powder (if you have a tempermental powder)...


Good information guys!!