Range Report Laminating dope cards - best baseline variables?

[300snipe]

So I'm laminating some dope charts that I printed from JBM - and my default one is currently using the altitude for my range and conditions for general fall weather:

50 degrees, 28.0 in HG, 25% humidity.

Wondering if I should stick with these variables or use some other baseline variables like 50% humidity or 0%, 30.0 barometer for calm weather, 0 degrees or 30 degrees? I know I have to compensate at the range for current conditions - so I want to have the most useful baseline on my dope charts.

What do you use?

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

The best thing to do is to print a Density Altitude dope chart. You might find this reference useful:

Making Ballistic Cards Using Density Altitude

 

[Dagsta]

Re: Laminating dope cards - best baseline variables?

Thanks Lindy I had lost that page in my bookmarks when my puter crashed!!

 

[300snipe]

Re: Laminating dope cards - best baseline variables?

I have the Altitude Density Compensator in my dope book - but I always shoot at 4200 feet so I don't really ever change that aspect. It's the humidity, temp, and barometer changes that I need to compensate for without using a handheld computer (which I have but I'd like to know/memorize the compensators for those values without a computer).

So I'm not sure what values to use for a baseline of those variables when I'm making the JBM charts. I can't make one for each iteration of combinations - it would be too much!

 

[vman]

Re: Laminating dope cards - best baseline variables?

Thanks for the link Lindy

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I have the Altitude Density Compensator in my dope book - but I always shoot at 4200 feet so I don't really ever change that aspect. It's the humidity, temp, and barometer changes that I need to compensate for without using a handheld computer (which I have but I'd like to know/memorize the compensators for those values without a computer)</div></div>

If you mean, by "Altitude Density Compensator", Taylor White's FDAC, then you don't really understand what density altitude is.

The FDAC, as well as the Density Altitude dope cards I wrote about, are precisely intended to allow you to compensate for temperature, humidity, and barometer changes <span style="font-style: italic">without a computer</span>. Density altitude is simply a single-number representation of air density calculated from temperature, humidity, and pressure.

It might be a good idea for you to go read my article again.

 

[300snipe]

Re: Laminating dope cards - best baseline variables?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body"><div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">I have the Altitude Density Compensator in my dope book - but I always shoot at 4200 feet so I don't really ever change that aspect. It's the humidity, temp, and barometer changes that I need to compensate for without using a handheld computer (which I have but I'd like to know/memorize the compensators for those values without a computer)</div></div>

If you mean, by "Altitude Density Compensator", Taylor White's FDAC, then you don't really understand what density altitude is.

The FDAC, as well as the Density Altitude dope cards I wrote about, are precisely intended to allow you to compensate for temperature, humidity, and barometer changes <span style="font-style: italic">without a computer</span>. Density altitude is simply a single-number representation of air density calculated from temperature, humidity, and pressure.

It might be a good idea for you to go read my article again. </div></div>

Great articles, thanks for taking the time to write those up. I think I get it now

I spent some time last night typing out data tables for "PressureAltitude_StationPressure", and "ICAOStdAtmosphere". Later this week I'm going to program that data into associative arrays for my fledgling scripts (I like programming things myself so I have a full understanding of the topic) and post when done. I'll release the code (python) under the new BSD opensource license so people can use it on their Android/Linux phones.

There's a thread going on over here about equations if you're interested. I'm still trying to find a couple of equations to finalize the ballistics app. http://www.snipershide.com/forum/ubbthreads.php?ubb=showflat&Number=2127543

 

[edwin907]

Re: Laminating dope cards - best baseline variables?

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">It might be a good idea for you to go read my article again. </div></div>

First I've seen of this article, terrific job! Very well done.

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

Thanks! I'm glad you found it useful.

 

[300snipe]

Re: Laminating dope cards - best baseline variables?

Here are the ones I was referring to:

59.0 Standard Temperature - F
29.92 Standard Pressure - in Hg
0.0 Standard Humidity - %
0.0 Standard Altitude - feet
1116.4499 Sound Velocity - ft/s
0.076474 Standard air density - lbs/ft^3

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

Well, that's the ICAO Standard Atmosphere baseline.

I'd choose a baseline that's closer to where you normally shoot.

However, if you print a density altitude dope card, a baseline pretty much becomes irrelevant.

 

[blakheaven]

Re: Laminating dope cards - best baseline variables?

Basically Density altitude (like most shooting) is a simple physics problem. (By the way us pilots deal with DA because an airport at 6000 AGL will act like an 8500 AGL airport on hot days) But I digress, DA is the phenomenon when temperature (increases or decreases) effecting the density of the molecules in the air- no duh. Pilots hate it because of increased take off rolls but shooters I would think would love it because in increase in DA would mean the molecules are spread out more providing less resistance which translates to flatter trajectories. Lindy is correct, the best way to prepare for DA (temperature, humidity BP) is do the same thing pilots do, make a DA chart. I am sure Lindy explained this way better than me but I always enjoy talking about the particle aspect of it.

 

[sobrbiker883]

Re: Laminating dope cards - best baseline variables?

Following with what Lindy's got all dialed in, I make a DA dope chart that matches the "usual" shooting at me hime range, and I have -2000 up to 15,000 in 1500-2000 increments in my dope holder on my rifles.

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

That'll pretty much cover anywhere in the world you might want to shoot a precision rifle, I'd say. (I did see some density altitudes around -4000 feet in the U.S. last winter, but I suspect there wasn't much shooting going on there.)

 

[sobrbiker883]

Re: Laminating dope cards - best baseline variables?

It doesn't take much more to have all bases covered (they all fit folded over in my holders), and the "be prepared" is one BSA lesson I try to use to this day

 

[RayDog]

Re: Laminating dope cards - best baseline variables?

I've found that I can leave a 7000AD card on my gun just about all the time and depending on conditions I can go a click more or less as needed.
But I also print out sets in 2000' intervals. I just always seem to forget to change them and know I can go from say

My 260 Dope for 7000 AD
500 yards- 7.75 MOA elevation and 2MOA wind for a 10 at full
1000 yards 22.8 MO elevation and 4.6 MOA wind

My 260 Dope for 11,000AD
500 yards 7.5 MOA elevation and 1.75 for wind.
1000 yards 21.7MOA elevation and 4 MOA wind

So at 4k AD change at 500 shouldn't make you miss a shot and at 1K we are only looking at 1 MOA in elevation and .6 in wind

Knowing this I can run a 7k card and adjust up or down pretty close to whatever the actual AD is

 

[sobrbiker883]

Re: Laminating dope cards - best baseline variables?

Compare your 7000 to 0 or -1500 and keep that in mind if you get to NorCal ever. I had a DA shift of about 3K snap my carrot at their long line when I shot out there.

We were all discussing what happened that we all needed an extra mil at 1K when one of our bunch said, "Oh yeah, you guys didn;t catch that front that rolled in?" Wasn't a storm, but we went from around 1500 to -1500 between shooting the 500 and 1K lines. That's what taught me to pay attention to DA, not temp.

Driving 13hrs and paying for a match, hotel and gas only to smack the top of the berm at 1K was a priceless lesson.

I've found that it seems its the DA drops that get you......and they can happen in a hurry at near the ocean.

 

[Lindy]

Re: Laminating dope cards - best baseline variables?

I was running the line at a Rifles Only match when we shot the 1000 yard target. Many of the rounds hit low. After everyone had shot, I asked, "Did anyone check the barometric pressure?"

The response was a lot of people smacking foreheads, and one guy who said, "Yes - after I shot."

The BP was 30.1 inches. It matters.