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How Much Does Temperature Effect Bullet Impact?

The Background
I got an email from a reader who was looking to order a CDS dial from Leupold, which requires certain information (including altitude, temperature, etc.).  He was concerned about what temperature to provide them. What if his dial said 80 degrees Fahrenheit and he was hunting in 40-degree weather?

The Question
What effect does temperature have on a bullet’s impact at reasonable hunting distances?

The Data
We’ll take a fairly common hunting round, the .270 Winchester with a 130 gr. TTSX bullet. The Barnes Vor-Tx factory load advertises a muzzle velocity of 3060 fps.  Using the Hornady Ballistics Calculator, we will set the altitude, barometric pressure, and humidity at a constant (Sea Level, 29.53 hg, 78 percent) and adjust temperature to determine the variance.

Bullet drop

Distance (yards):        200      300      400      500

100 Deg F                   2.8”     10.7”   24.6”   45.4”

80   Deg F                   2.9”     10.9”   25”      46.3”

30   Deg F                   3”        11.2”   26”      48.6”

0     Deg F                   3”        11.5”   26.7”   50.3”

The Results
As you can see from the numbers, temperature has a minimal effect on bullet drop at reasonable hunting distances. All things being equal, bullets will drop more at lower temperatures, but the difference is negligible. (Note: Changes in temperature are often accompanied by changes in humidity and pressure that can give you different results)

The Ruling
Temperature is a non-factor for 98 percent of shots in big-game hunting. Even with a temperature swing of 50 degrees, the difference in point-of-impact is only an inch at 400 yards. I don’t know about you, but I can’t hold an inch at 400 yards under hunting conditions. If you’re ordering a custom dial, use a reasonable “average” temperature for the locales where you’ll be hunting and put it out of your head.

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8 Responses to How Much Does Temperature Effect Bullet Impact?

Doug Gary wrote:
October 31, 2013

Tempertaure dont effect a bullet that much at close distances, but get out to 1000+ yrds and it effects it alot more

Bob wrote:
July 12, 2013

KW, As Kevin stated there is a lot more to this than meets the eye. Using the same calculator and your test criteria I ran a spread (6) common cartridges from .223 to .308 diameters at standard velocity's and came up with following: While most average around 1/2 to 5/8 minute in impact point (IP) variation from 0 to 100 degrees, some are far worse. For instance a .223 with a 55gr .250 BC, at 3200 fps IP will change 9.2', almost 2 minutes. Even further to the extreme is the old 3040 Krag, (don't laugh people still shoot them) with a 180gr, .501 BC at 2300fps the old rifles IP change is only 6.4', not too bad for an old girl. However when a .271 BC bullet is used the IP suddenly jumps to 17.6', or approximately 3 1/2 minutes. So from my perspective without having substantial ballistic information to say that the effect is minimal would be hazardous at best. As for the Leupold CDS, I have one on my favorite rifle. I provided them with actual chronograph velocities, BC, average altitude, and temperature and couldn't be happier, it shoots better than I can hold it, what more could you ask for...Bob

Kevin Schwinkendorf wrote:
July 11, 2013

According to the Sierra Reloading Manual (I still have the 3rd Ed), local conditions (T, P, humidity, altitude) affect the ballistic coefficient in known ways, using their mathematical correlations. At higher altitude, the reduction in air density is a direct factor in the drag function in the equations of motion (it multiplies the G1 function directly). A shift in the speed of sound also correlates with altitude (the slope of the G1 function is maximum around Mach 1). Finally, yes, ambient temperature can affect the muzzle velocity according to what kind of powder you have. There is a useful table in the Speer #11 reloading manual that provides a 'best estimate' for most powders, but there can be significant departures from these predictions for particular cases. I have written a ballistics computer code that incorporates all these effects, and have found that to a certain degree, some of these factors tend to cancel each other out, but the net effect may still affect the predicted bullet drop by up to 10[%]. A bigger factor is correcting for uphill or downhill shooting, if the angle is greater than about 25 degrees or so, but then again, even this factor is really only significant for long-range shooting, like 300-400 or more yards, depending on the cartridge in question. If you are zeroed at 200 yards, none of these factors will have much affect out to 300 yards or so. However, military snipers, if they are trying to take a shot at 1500 yards, yes, these factors could be critical. Another factor is the Coriolis effect, but this only becomes significant beyond 1000 yards (at ranges less than that, Coriolis effects amount to less than an inch).

KW wrote:
July 11, 2013

Bob- I understand your concerns regarding the application of ballistic software in the field. I have routinely used rifles zeroed in 90 degree weather here in Florida in freezing tempearatures in the mountain west with no discernable shift in impact. Using the Hornady data helps quantify the findings that I've made in the field. The moral of the story is, unless you're shooting at extreme range, you'll be fine.

Bob wrote:
July 11, 2013

I understand the air density and temperature thing on paper. What I'm curious about is the possible effect powder burn rate could have across the same temperature range used. I use the Hornady calculator regularly, but never take some of the results for granted until I check them myself under actual field conditions. I think perhaps you should qualify your statement a little more so not to mislead.

Ernie White wrote:
July 11, 2013

I have my deer rifles sighted in for 100 yard. Most of my shots were between 50 & 75 yards. I have always hit my target. Win. 30-30 & a 30.6

Wayne Chmielecki wrote:
July 11, 2013

Thank you for your article. I was always curious if temperature had a significant effect on bullet performance, but never tested it. I reload my own ammunition and was concerned enough to change my powders to Hodgdon's extreme powders to eliminate that possibility, especially since I develop my loads in the summer at 80 degrees and then hunt in 30 degree weather. Thanks for removing some of that concern.

Jim Nelson wrote:
July 10, 2013

I wonder if info wanted was also penetration At various temps.