When do I need to care about Dens. Alt. changes?

[newgunguy3]

I'm taking a 5 day LR training class (100 - 900 yards). Ive been before and know over the course of the day the temperature will change almost 40 degrees. This has an effect on D.A. From the DOPE I have from the previous class, the day will start around 2300 and go to 4000 feet. My question is how much does this really change the potential ballistics for a 308 at these distances? Sure, if I was shooting 1 mile plus I'd be concerned but how much of an impact in terms of inches shift will a bullet move if shot at 2000 DA and 4000 DA? I'm trying to decide if I have to be maniacally obsessive about recording every string and it's DA because if I shoot a distance at 8 am with one DA then at 4 PM with a 1500 ft DA shift, my bullet will be way off.

Thanks for your insight.

 

[Blowby]

11-12" based on your load @900 yards from 2300-4000DA.

 

[uncoffeed]

Get a Kestrel Drop and use it with Strelok on your phone/device.
It's still a good idea to record DA and resultant drops occasionally, just to have some easy-to-read paper info. Also a good idea to measure temp and DA along with your velocity at several different temps. A Kestrel Drop (or WeatherFlow or standard Kestrel or whatever) takes the difficulty away.
I generally update my Strelok info every time my Kestrel shows a change of 500DA or 5*F. It's easy and a good habit.

 

[Diver160651]

With my 6.5 just as a logic example.

At 600 with a 30* temp swing I get about .o5 mil difference. That also is about 2 k da change.

I look at the temp issue in blocks. If I expect low of 70 and a high of 90- I’ll set on 80. Baro doesn’t really change much unless your climbing a Mountain.

In this case all three call for 3.2mil in the real world. By 900, you might start to add and subtract .1. My 80* call is 6.3 bracketed by 6.37 & 6.25; but even then, .1 isn’t going to be a miss at most steel matches

Now if I go for 600 at a 50* swing 50-100 set to 75, I get 3.2 but at 100* it is asking for 3.15, at 5o* 3.25. So while it looks to be .1 change my 75* call is still as close as my scope can adjust.

Sure by 700 i’ll + .1 off -.1 for the Extremes. But if I was expecting more than a 30* swing I run two cards.

Hope this logic makes sense, but most people inside 1000 get a bit paralyzed by the tools, is my only point.

But, because it is a class it would not hurt to have a few preprinted drops charts..

Edited to add: You'll get hosed more my mishandling your ammo and internal ballistic due to extreme chamber temps - especially if you using known temp sensitive powders.. But powders like Varget for a 308, are harder to miss-handle.

 

[Deleted member 113831]

I'm taking a 5 day LR training class (100 - 900 yards). Ive been before and know over the course of the day the temperature will change almost 40 degrees. This has an effect on D.A. From the DOPE I have from the previous class, the day will start around 2300 and go to 4000 feet. My question is how much does this really change the potential ballistics for a 308 at these distances? Sure, if I was shooting 1 mile plus I'd be concerned but how much of an impact in terms of inches shift will a bullet move if shot at 2000 DA and 4000 DA? I'm trying to decide if I have to be maniacally obsessive about recording every string and it's DA because if I shoot a distance at 8 am with one DA then at 4 PM with a 1500 ft DA shift, my bullet will be way off.

Thanks for your insight.

The change in lighting throughout the day will likely make much more difference than any of the environmentals affecting DA. If the sun is out you will see changes for sure, but it won't be anything you can solve with a ballistic program.