Tuning with Density Altitude

B

Bart

Member
This is my opinion and you can take it for what its worth … but if you are trying to tune your rifle by tracking and adjusting off of Density Altitude (DA) you are barking up the wrong tree. I have tracked DA changes for every group that I have shot in the past 3 months. I have tracked it from Bradenton, Florida to Phoenix Arizona and down to Georgia at the Shamrock, not to mention a good bit of shooting on my own range in Kentucky. It doesn’t work. Not only does it not work it’s not even a very good indicator of where your load should be or which way to adjust.

Here is an example…The first day of the Cactus the DA changed 1100 ft between the 1st and 5th match of the LV 100. I never change my load and shot an 1810 agg. In the afternoon I dropped my load .3 tenths and gun stayed in tune. The DA change a total of 2000 feet by the time I loaded for the last match of the day. My last group was a .110.

Maybe tracking and changing loads with DA works in some parts of the country but in the 7000 miles I have traveled this year it hasn’t been the answer.

Bart
 
What powder weight do you use Bart ?

I have been watching the DA changes while using loads in the 30 grain N133 range and it seems that if there is a reliable correlation it requires a much smaller change than the 0.3 grains per 500 feet that Gene Beggs has mentioned in relation to a load around the 29 grain range.

I had a load shooting nicely at DA of 0 feet and a powder weight of 30.4 grains. That load was shooting very well indeed, sub 0.10 with 4 in around 0.05. 30.2 shot just about as well with a three shot test group of 0.05 and a 5 shot group of something like 0.16 and as I went lower the groups opened up in the vertical to about 0.3 when as low as 29.4 grains.

A few weeks later at another range a DA reading of around 1000 feet needed a load of around 30.1 grains to shoot and 29.8 and 30.4 would do OK but were not consistently as good as a load in between. When I read the wind right the 30.1 grain load was shooting nice and flat at 200 so seemed to be in decent tune, I managed a 0.35 at 200 when I got the wind reading right.

If that means anything the 1000 feet DA needed only 0.3 grains.

I don't mean to try and tell you anything about load tuning but remember that Genes method involved the tune coming back around every 2000 feet DA change. In my case if the DA went as high as 2000 feet it would seem I could drop back by another 0.3 grains to 29.8 or go back up the same 0.3 grains back up to 30.4 grains again.

I haven't messed with this enough over a wide range of DA change or over a large change in elevation or humidity but there does seem to be some correlation between the DA and the powder weight to keep in tune, just not the correlation Gene stated for a 29 grain load.

If for example 30 grains needs a 0.3 grain change per 1000 feet it could easily be that for a change of say 500 or 600 feet the change needed to be in PERFECT tune could be so small as to be lost in the noise. If the DA changed by say 1500 feet you'd nearly be back to the next DA level that the load would be in tune for. That sssumes that Genes number of 2000 feet between "nodes" is correct at the upper window. If that is anything like what is happening and it is only possible to ever be off tune by say 0.3 grains when using an upper window load it would be feasible to shoot some pretty respectable groups and not see the effect of the off tune state unless the conditions were really good.

Just thinking out loud as much as anything, I sure respect your ability to shoot and tune and don't doubt what you have observed.

Bryce
 
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Bart, although density altitude (DA) affects the way our rifles tune and shoot it is by no means the only factor that influences in-bore elapsed time.

The barrel begins to vibrate as the bullet travels down the bore; the muzzle comes to a complete stop at the top and bottom of its swing. In order to be "In tune" the bullets must exit at one or the other of these stops. Many believe it is best for the bullets to exit at the top rather than the bottom, although I have not found that it matters. With my tuner, I can move the exit point from top to bottom with one revolution.

When teaching people to use the tuner, I no longer place such emphasis on density altitude. I explain it, but I now emphasize how important it is to let the rifle tell you when it needs a tuner adjustment. With my tuner, the most you can be out of tune is one half turn. A three shot group on the sighter will tell you whether you need to make a half turn or a quarter turn. If the group shows only one bullet hole of verticle, you are a quarter turn out of tune. Two bullet holes of verticle indicate the need for a half turn.

At the Super Shoot, I will be happy to demonstrate the tuner to those who are interested. It really is quite simple!

Best regards

Gene Beggs
 
Lou,

If it is a Kestrel 4000 the trick is to go into the set up menu and turn off all the readouts for the pile of things you don't need to know.

I set up a "user screen" to show DA, Tem and humidity and everything else is turned off, if you cycle through the readouts you just get three.

There is a messy little set up for elevation and pressure but after having no luck getting them to be stable I read that the Kestrel doesn't use these readings for DA, it uses actual measured "station pressure" not the one corrected to sea level.

This makes it easy as hitting the on button to get a reading of the three most used items, if you choose to try it.

Bryce
 
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Air density meter life coach

There are many things that the air density meter can do other then merely adjusting loads for shooting or twisting a tuner. It can be used to plan your whole daily calender. As an example if the air density is higher then normal don't get out of bed. You could suffer a flossing injury or pull a muscle fighting too high a density. If the air density is lower then normal be cautious in moving too fast. You might not be able to stop without the extra cushion of normal air density. If the air density is very low talk extra loud on your cell phone as sound waves travel slower in less dense mediums. If the air density is high you can whisper into the cell phone. Just think of all those obnoxious people talking too loud on their cell phones in hospitals, church, funeral parlors, bars and other places of worship. If only they had an air density meter they would be socially responsible and probably also get extra carbon credits. Just don't give one to your spouse. The new excuse would not be a headache but "The air density isn't right". Tim
 
Tim that was the best definition of DA usefulness I've read.
But I don't know what to do now...
Should I tip over in my chair?
 
BJS6/Bryce,

I use V133. A 2001 and 2005 batch. I also use 8208. What weight do I use? I use whatever load the gun needs. It can be anywhere from 27.9 to 30.5. When I go to a shoot I get the load pretty quickly. There are normally 4 to 5 members of the “Alabama Mafia” working together to figure it out.

I am not trying to discredit Gene. I’m just reporting what I have observed/learned. If you follow a DA meter (as has been posted) it doesn’t work. At least not the places I have been.

Gene,

I think you are doing a lot of great work down in Texas. Keep it up. I think you can help a lot of shooters. I am also very sure if you would have been able to make Phoenix (I know you planned to but couldn’t) and followed your formula for DA you would have taken your rifle out of tune. You may have been able to save yourself if you kept to the use the tuner like a “focus ring”, but not by following DA. I would keep teaching the “focus ring” method and leave DA out of it.

As for tuning/shooting I’m not into theories. I don’t care about how/why stopped muzzles work or barrel vibrations or where the bullet exits the barrel. Quite frankly my eyes start to glaze over reading or listening about it. All I care about is does it work in the real world of competitive benchrest.


BTW…I am of the opinion that tuners are a thing of beauty. I have 3 different types of tuners currently in my possession.

Tim,

You are right on track brother!

Bart
 
Bart. Gene said:
Thank you Bart. I agree. It is best to think of the tuner as a "focus ring" adjusting only when the rifle tells us to do so. This greatly simplifies things and eliminates the need to figure DA. We think nothing of fine tuning the focus on our scope; now, with the use of a tuner, we can 'focus' the barrel in the same way by firing a three shot test group on the sighter.

See you in Ohio

Best regards

Gene Beggs
Click to expand...
 
About DA

I know what DA is and does, but I am not sure which part of the equation it really effects to cause the result.

Does effect of DA change the combustion process of the powder.

Or is it the air that is in the barrel.

Or is it the air that the bullet is traveling through.

Or is it a combination of DA and temperature of the barrel (like if you cook a shot or if you shoot so many sighters that the barrel is really hot).

If it is the combustion of the powder, is it effected most by temperature, humidity, air density or some combination.

Also, if it is the air in the case, is it the air when it was loaded, like if you preloaded in one DA condition and fired the shot later in a different DA condition.

Sorry about all the crazy questions, but I just gots to know if I am going to depend on DA for my load adjustments.

Thanks.

Larry
 
I've been using a Kestrel 4000 since Nov. 2002...

at every tournament I've attended. At these tournaments, every time I returned from shooting a group, in practice and competition, I've recorded the DA, RH, Temp. and DP and number of shots. At the start of the morning, I also record the barometric pressure and again at the start of the afternoon shoot. Being an old, retired CPA, I'm still nuts about maintaining good records.

During this time I've attended about 12 tournaments/yr. in AZ, UT, WY, CO, NM, SD, TX, MO, KS, WA, MT and OH. After each tournament, I sit down with my targets and notes on wind conditions and the info above and try to analyze my results, trying to perfect a methodolgy for load development. So I have plenty of experience in both time and areas around the U.S. From sea level to 6700', from hot-dry to hot-humid and everything in between.

And all of this is to state that I completely agree with Bart and others in that I have never been able to correlate DA with any load matrix. It just isn't there. Temp. and RH/DP yes, but a direct relationship with DA eludes me. I do like the Kestrel and use while hunting and fishing too, but the little Radio Shack temp/humidity gadget is all one really needs.

Anyhow, this is my long-winded story and I'm sticking with it!

Jim
 
Air Density

Tim,
"Air density meter life coach".
I can see why you hold the title.

Best,

Dan Batko
 
Mother of all Elves lacking in density

Please note the rapid plummet into the dregs of scientifically acceptable behavior that this thread has plunged. Now there are references to magical thinking dating back to the Druids (Mother of all Elves) and very thinly veiled insults ( lacking in density). There is serious discussion about alchemy (changing air density into gold). Doubting Thomas's, zealots and mystics have run rampet in print. Given the brilliant, but always ultimately bent, character of most benchrest shooters I am not surprised in the least. Tim
 
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Dr Tim

How much "density altitude" do you plug into that "fart machine" you got me with at Tomball???.
Tell "Dickey P" I am working on that Rap..........jackie
 
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