Temperature Effects

Winston · July 16, 2002, 09:53 AM

Does anyone have a field expedient formula for estimating
the effects of temperature on bullet ballistics for ranges
100-1000 meters on Federal .308 168grain match ammo?

In MOA or Mil hold-overs?

Thanks

Rob01 · July 16, 2002, 09:56 AM

The old rule of thumb is 1 MOA change for every 20 degrees of temp change. Although the best way to find out for sure is to shoot the temps and log them in your logbook so the next time you need them you know exactly where it will hit.

C.R.Sam · July 16, 2002, 12:52 PM

Like Rob01 says.....shoot it and log the results.
Each rifle unique.
Barrel temp will also make a difference.

Sam

Jamie Young · July 16, 2002, 05:56 PM

Don't forget "humidity" also. That makes as much of difference as temp does.

Mo_Zam_Beek · July 16, 2002, 06:31 PM

They aint lying. If I remember correctly ammo is tested at 59 degrees by the manufacture (baseline MOA readings). Elevation - changes greater than about 1,400 ft - check zero, temp changes, humidity all play a role.

One spot that I like to shoot at is about 3k higher than town, and with some heat I am 20" or so high at 600 from the range in town.

It all makes a difference.

Good luck

rick_reno · July 16, 2002, 07:58 PM

I have an old ballastic program from Oehler (they make chronographs - this program might have come with the chrony, I don't remember) that has input for temp, humidity, elevation and a bunch of other stuff. I'm sure some of the newer programs out there would help you with what you're looking for.

Jamie Young · July 16, 2002, 09:19 PM

Play with this

http://internet.cybermesa.com/~jbm/b...raj_basic.html

Rob01 · July 16, 2002, 09:42 PM

Soda, actually humidity doesn't have that great of effect as once thought. More tests have been done and found that humidity effects are so small they aren't even worried about. Depending on what ballistics program you run it's only a couple of inches at 1000 yards.

Jamie Young · July 16, 2002, 09:50 PM

What about 100% Humidity...... like rain???

Or frozen humidity...like hail??

Winston · July 16, 2002, 09:59 PM

Given temperature clear impacts bullet trajectory in the vertical
plane:

1. How does temperature affect hold over calculations for windage? Say a 10 mph wind for a 600 meter shot results
in X MOA holdover. Will a 20 degree temp increase effect
hold over as the "wind" is less dense, thus pushing the bullet
less

Jamie Young · July 16, 2002, 10:21 PM

Its all about "air density." So, you've answered your own question.

Don't get too caught up in calculations. A lot of this stuff is knowing enough to make a best guess. But I'm still a rank amatuer at this stuff.

Andy Chadwick · July 17, 2002, 01:48 AM

Somewhere I read that temperature effects on interior ballistics change POI much more than the effect on external ballistics. True?

Rob01 · July 17, 2002, 06:10 AM

I've shot at 600 yards in the rain and my come ups were the same as if it were dry out so Rain doesn't have that much effect. Haven't shot in freezing snow or hail yet so when I do I'll find out but I'm not thinking it will be that much more off unless you hit one of those softball size hail balls.

As far as wind, a 10mph wind is a 10mph wind whether it's 40 degrees or 90 degrees. You will have to adjust your elevation but your wind adjustments or holds if you don't adjust with the windage knobs will be the same no matter the temp. Like Sodas said, don't worry too much about the calculations. I don't know everyone elses background so maybe a BR or highpower shooter might have different info but I'm a tactical shooter and those are how I get on my target and they have worked so far.

July 16, 2002, 09:53 AM	#1
Winston Senior Member Join Date: May 6, 2001 Posts: 141	Temperature Effects Does anyone have a field expedient formula for estimating the effects of temperature on bullet ballistics for ranges 100-1000 meters on Federal .308 168grain match ammo? In MOA or Mil hold-overs? Thanks

July 16, 2002, 05:56 PM	#4
Jamie Young Senior Member Join Date: April 7, 2000 Location: SE/PA Posts: 4,834	Don't forget "humidity" also. That makes as much of difference as temp does. __________________ Find out about Gun Shows and Training activities. www.TheRallyPoint.org Get your gun club involved!!

July 16, 2002, 07:58 PM	#6
rick_reno Junior member Join Date: May 28, 2002 Location: Idaho Posts: 917	temperature effects I have an old ballastic program from Oehler (they make chronographs - this program might have come with the chrony, I don't remember) that has input for temp, humidity, elevation and a bunch of other stuff. I'm sure some of the newer programs out there would help you with what you're looking for.

July 16, 2002, 09:19 PM	#7
Jamie Young Senior Member Join Date: April 7, 2000 Location: SE/PA Posts: 4,834	Play with this http://internet.cybermesa.com/~jbm/b...raj_basic.html __________________ Find out about Gun Shows and Training activities. www.TheRallyPoint.org Get your gun club involved!!

July 16, 2002, 09:50 PM	#9
Jamie Young Senior Member Join Date: April 7, 2000 Location: SE/PA Posts: 4,834	What about 100% Humidity...... like rain??? Or frozen humidity...like hail?? __________________ Find out about Gun Shows and Training activities. www.TheRallyPoint.org Get your gun club involved!!

July 16, 2002, 09:56 AM	#2
Rob01 Senior Member Join Date: October 21, 2000 Posts: 455	The old rule of thumb is 1 MOA change for every 20 degrees of temp change. Although the best way to find out for sure is to shoot the temps and log them in your logbook so the next time you need them you know exactly where it will hit.

July 16, 2002, 12:52 PM	#3
C.R.Sam Senior Member Join Date: October 29, 1999 Location: Dewey, AZ Posts: 12,858	Like Rob01 says.....shoot it and log the results. Each rifle unique. Barrel temp will also make a difference. Sam

July 16, 2002, 06:31 PM	#5
Mo_Zam_Beek Senior Member Join Date: August 20, 2001 Posts: 308	They aint lying. If I remember correctly ammo is tested at 59 degrees by the manufacture (baseline MOA readings). Elevation - changes greater than about 1,400 ft - check zero, temp changes, humidity all play a role. One spot that I like to shoot at is about 3k higher than town, and with some heat I am 20" or so high at 600 from the range in town. It all makes a difference. Good luck

July 16, 2002, 09:42 PM	#8
Rob01 Senior Member Join Date: October 21, 2000 Posts: 455	Soda, actually humidity doesn't have that great of effect as once thought. More tests have been done and found that humidity effects are so small they aren't even worried about. Depending on what ballistics program you run it's only a couple of inches at 1000 yards.

July 16, 2002, 09:59 PM	#10
Winston Senior Member Join Date: May 6, 2001 Posts: 141	Follow up question Given temperature clear impacts bullet trajectory in the vertical plane: 1. How does temperature affect hold over calculations for windage? Say a 10 mph wind for a 600 meter shot results in X MOA holdover. Will a 20 degree temp increase effect hold over as the "wind" is less dense, thus pushing the bullet less

July 16, 2002, 10:21 PM	#11
Jamie Young Senior Member Join Date: April 7, 2000 Location: SE/PA Posts: 4,834	Its all about "air density." So, you've answered your own question. Don't get too caught up in calculations. A lot of this stuff is knowing enough to make a best guess. But I'm still a rank amatuer at this stuff. __________________ Find out about Gun Shows and Training activities. www.TheRallyPoint.org Get your gun club involved!!

July 17, 2002, 01:48 AM	#12
Andy Chadwick Member Join Date: March 2, 2002 Posts: 33	Somewhere I read that temperature effects on interior ballistics change POI much more than the effect on external ballistics. True?

July 17, 2002, 06:10 AM	#13
Rob01 Senior Member Join Date: October 21, 2000 Posts: 455	I've shot at 600 yards in the rain and my come ups were the same as if it were dry out so Rain doesn't have that much effect. Haven't shot in freezing snow or hail yet so when I do I'll find out but I'm not thinking it will be that much more off unless you hit one of those softball size hail balls. As far as wind, a 10mph wind is a 10mph wind whether it's 40 degrees or 90 degrees. You will have to adjust your elevation but your wind adjustments or holds if you don't adjust with the windage knobs will be the same no matter the temp. Like Sodas said, don't worry too much about the calculations. I don't know everyone elses background so maybe a BR or highpower shooter might have different info but I'm a tactical shooter and those are how I get on my target and they have worked so far.