Effects of Temperature and Elevation

[Blkram]

I have had this question rolling around in the back of my mind for quite some time, and this weekend, I awoke thinking of it again as I was about to head to the range to sight in a couple new rifles and test out some new ammunition in a couple of other...
What is the actual impact on a bullet's flight due to changes in temperature and elevation when hunting?

Well, it took me most of the weekend to crunch the numbers, but for some of my more common cartridges used for hunting, in my region, and the various elevations I have hunted, and the average monthly temperatures in which I hunt, here are the answers to my question:

Over the past 38 years of hunting big game, I have taken 119 animals, in what I will call the flat lands and the mountains, at distances ranging from 5 to 475 yards. The average shot distance has been132 yards.
The elevations I have taken game at ranges from 2200 to 6000' ASL. The average is at 3200' ASL. (The average flat land elevation has been 2600' (61% of game taken) and 4400' (39% of game taken) for the mountains.)
The temperatures in the areas I have hunted has ranged from approx. -30 degrees below zero to approx. 30 degrees Celsius above zero. The average monthly temperatures have ranged from -6 degrees C (21 F) below zero in November to 27 degrees C (80 F) above zero in August, withe an average of 6 degrees C (43 degrees F).

I have been using 2200' ASL in the Hornady Ballistics Calculator, and a temperature of 10 degrees C (50 F) to calculate the ballistics of various cartridges (chronied and factory spec velocities) for quite some time now. I use a 200 yard zero, and 100 yard increments out to 500 yards (the distance I can shoot at my range for practice), and therefore my limit for shots on wounded game if needed. Of all the game taken to date, I have less than a handful of game taken at over 400 yards. (The longest shot was under estimated at the shot, and verified afterwards).
I looked at 7 different cartridges that many use today for hunting, and chose the ones using the new Federal Terminal Ascent ammo just so I had a consistent hunting bullet for comparison. These include the following: 6.5 CM, 6.5 PRC, 270 Win, 270 WSM, 7mm Rem Mag, 7MM PRC and 300 WSM.
The variance of drops in elevation from my usual calculation of 2200' and 50 F, ranges from 1.6" to 2.8" at 500 yards!

Variances of drops @ 500 yards, from 2600 to 4400' ASL and 21 to 80 F, using the 200 yard zero is:
-6.5 CM 130 gr(24" barrel) is 2.4"
- 6.5 PRC 130 gr (24" barrel) is 2"
-270 Win 136 gr (20" barrel) is 2.8"
-270 WSM 136 gr (23" barrel) is 1.9"
-7mm Rem Mag 155 gr (26" barrel) is 1.6"
-7MM PRC 170 gr (24" barrel) is 1.7"
-300 WSM 200 gr (23.5" barrel() is 2"

Not as big a variance in drops as I might have imagined! (And of course, the variance is less for 400 yards, my self imposed limit today.)
And I know that my shooting is not such that I am going to see that big a difference at this range, especially since I do not shoot at unwounded game at 500 yards anyways.

Moving forward, I will be using 3200' ASL and 43 F for my Hornady Ballistics Calculator when calculating, as that averages out with the ballistics of these cartridges in my rifles for the game I hunt, in the months and locations I hunt, in order to give me the closest overall average drops for sighting in and shooting, to effectively take game in the places I hunt regularly.

Have any of you looked at this for what you shoot, and where/when you hunt?

 

[Slimfinn]

I've looked into it, not as indepth as you have. Like you we can have a significant tempature and elevation differential between summer range shooting and hunting season between the plans and mountains. The avarage I typically punch in to use is 5,000ft and 30F when I am reviewing data to determine what to expect.

 

[xphunter]

It is always a factor for me.
I always put in the atmospheric data

 

[SJB358]

It is always a factor for me.
I always put in the atmospheric data

Same here. I shoot all summer at 1500 ft asl. Elk are at 8-11k so I rework my zeros to correlate with elk hunting when I’m using them for such.

 

[Bruce Mc]

My load work up and sighting is generally done at around 50' of elevation and from 80-100 deg f. I could use up more brain cells than I can afford to give up worrying about the difference out to 400 yds when I'm hunting most anywhere else, but I still do. I set my drop tables at 5000' of elevation and 40 degrees F.

 

[truck driver]

I'm with Bruce Mc on the loss of brain cells trying to figure it out, so I let someone else do it for me who has a ballistic app when I hunted at higher elevations but tried to do my load development in the fall for big game rifles and spring for varmint rifles.
Scotty helped me out when I went to Montana and when I test fired my rifles there they were spot on.

 

[Bruce Mc]

Y'all should try a ballistics program that operates in excel. It's called pejsa and is available for download from jacksonrifles.com. it's operation is so intuitive even a caveman could use it. And it's free.

 

[Blkram]

I have since also crunched the numbers for all of my rifles that I use Nosler AccuBond bullets in (which is all but the varmint cartridges and 22's), as it is still my favourite bullet overall, and takes me from the 25 cal to the 375 cal. (Still wish they would make a 350 gr for the 416!)

It was definitely an interesting exercise, and fascinating to note how little impact the temperature and elevations had on ballistics over a 3800' change in elevation and 60 degree variance in ambient temperatures, on hunting ammunition for my region.
With the variance of 2.8" being the largest variance, and due to this normally flat shooting cartridge (270 Win) being used in a carbine, which isn't going to be the rifle carried on a mountain hunt anyways, and I am not likely to be taking many shots at 500 yards on unwounded game from field positions, plus or minus a couple of inches isn't going to make as big a difference as originally thought. (Note that I am not a competition shooter, just a hunter! )

When I can consistently hit center of mass on the metal pig target someone placed at 500 yards on my local range, with my various rifles, I am quite happy!
I am confident that good shots on mountain sheep, mountain goat, deer and antelope as far out as 400 yards are going to hit their intended marks!

And even if I were tempted to take a maximum range shot of 500 yards at game in the mountains (sheep or goat), using the 7MM PRC, and using my new average of 3200' elevation at 43 degrees F to zero the rifle, the variance between using the 170 gr Terminal Ascent (BC of 0.646) ammo at 2950 fps and the 175 gr ABLR (BC of 0.648) ammo at 3000 fps (closest in comparison and most likely to be used on the hunt), the variance between these two ammunitions from my original 2200' elevation and 50 degrees F is just 0.7" and 0.8" in drop at this distance respectively.

The variance numbers @ 400 yards are 0.3" for both! (my self imposed limit for shots on unwounded game from field positions)
And my shooting is such that from field positions, I am unlikely to notice the difference in actual shot placement on game at his distance! (And my longest shot to date on mountain game has been 300 yards)

While I have the capacity to accurately place shots on game at this distance with most of my rifles, I may not have to shoot that far. But is it confidence inspiring to know that I can if I should need to! And this makes a huge difference, as the annual practice keeps that skill sharp and confidence high!

 

[clearwater]

I find temperature comes into play on 2nd and 3rd shot when the temps approach 100' F.