Temperature effects

[Oklahunter1]

I am wondering how temperature effects powder. If your shooting say at 500 yards at 45 degrees then you shoot same load at 500 yards at 85 degrees will there be a shift in your groups?

 

[rammac]

Yes

 

[rammac]

You have two factors that are affected by temperature change.

The powder
The air density

Most powders produce more energy as their temperature increases.
Air density decreases as temperature increases.

The effect is that as the temperature increases the bullet's velocity will increase and the point of impact will be higher.

In general, at 500 yards, my .308 using a 180gr bullet will have about 3 to 4 MOA less drop at 85 degrees compared to 45 degrees.

 

[LaHunter]

You have two factors that are affected by temperature change.

The powder
The air density

Most powders produce more energy as their temperature increases.
Air density decreases as temperature increases.

The effect is that as the temperature increases the bullet's velocity will increase and the point of impact will be higher.

In general, at 500 yards, my .308 using a 180gr bullet will have about 3 to 4 MOA less drop at 85 degrees compared to 45 degrees.

Are you sure you are seeing a difference of 3-4 MOA at 500 yards? That is 15-20" difference in POI. Air density change is not going to make that much of a difference. If your values are correct, there is something else dramatically off. Some powders are temp sensitive, and the 80 degree range is where the effects start to show up

 

[Oklahunter1]

You have two factors that are affected by temperature change.

The powder
The air density

Most powders produce more energy as their temperature increases.
Air density decreases as temperature increases.

The effect is that as the temperature increases the bullet's velocity will increase and the point of impact will be higher.

In general, at 500 yards, my .308 using a 180gr bullet will have about 3 to 4 MOA less drop at 85 degrees compared to 45 degrees.

So if I'm trying to get the Dope on my load for hunting season I need to wait till the temperature drops? At what temperature will the effect be minimal?

 

[rammac]

Are you sure you are seeing a difference of 3-4 MOA at 500 yards? That is 15-20" difference in POI. Air density change is not going to make that much of a difference. If your values are correct, there is something else dramatically off. Some powders are temp sensitive, and the 80 degree range is where the effects start to show up

Yup, I should have said 0.3 to 0.4 MOA

 

[rammac]

So if I'm trying to get the Dope on my load for hunting season I need to wait till the temperature drops? At what temperature will the effect be minimal?

Just use a ballistics engine that includes ambient temperature as an input. Create a ballistics chart now and adjust it using your estimated temperatures and then verify the estimated drops with a few test shots when you get to your hunting site. If your tests shots seem off then record the proper values on your chart.

I recommend testing at the hunting site at your zero range and then in 100 yard increments to as far as is reasonable with the environment you are in. You shouldn't have to shoot more than 4 or 5 shots.

 

[Jeffrey Van Zandt]

I am wondering how temperature effects powder. If your shooting say at 500 yards at 45 degrees then you shoot same load at 500 yards at 85 degrees will there be a shift in your groups?

that is why a kestrel 5700 is a good thing to have

 

[BrentM]

Air density decreases with temperature increase. It's exactly why us pilots have issues in hot temps, loaded to max, and short air strips.

Others have already said it but you have internal ballistics and external ballistics working against you at all times. To see the shift of 3-4 I'd say you have a very unstable powder type and charge or you have parallax issues or maybe all the above. I'd definitely start with rezero the rifle in the hotter temp and rule out zero shift issues. While doing so I'd chrono the load. Watched my buddy shoot factory 223 ammo last night with 160 FPS es. Made for hitting steel at 500 really difficult.

 

[redneckdan]

Ran the numbers on my 6 creed hunting load and at 1000yds from 0f to 100f the difference is .7 mils.

A more realistic example for hunting situations, 40 - 80F @ 500yds is .1 mil. This is using that evil ball powder stuff where the bullet barely comes out the barrel @ 32F or your gun will blow up if you shoot it at 100F....or so they say...

 

[Tiny Tim]

Agree with all above. Much is dependent on powder. Some are more drastically affected by temp than others. Alliant has a few relatively temp insensitive powders as are the Hodgdon extreme line and the Enduron powders.

 

[Zymurgist]

I am wondering how temperature effects powder. If your shooting say at 500 yards at 45 degrees then you shoot same load at 500 yards at 85 degrees will there be a shift in your groups?

you need to get out and shoot at 17, 65 & 100 degrees. When the relative humidity is 20%, 90% or in between. When the wind is 10 knots in your face or 3 knots coming from the your right. When it's snowing or when it's raining. If you're above or below your target. All the while writing it into your dope book. Then you'll know how the elements affect your shot.

 

[LVJ76]

Some powders are affected and some aren't, and some more than others. As @Tiny_Tim mentioned, there are some that wont be affected by the rise or drop in temperatures. Even 22lr ammo is affected by temperatures.

As an example, shooting silhouette with my 7mm-08 I use IMR-4350 with 150gr Sierra Matchkings. Not a temp stable powder but also no too temp sensitive. If I start the match at 9 am at say 80 degrees, at the 200m targets I'll have no issues, but by 2:00 pm when its 105 degrees or higher and shooting at the targets at 500m I'll be hitting 5" to 7" high. Now I know this by experience from many years of shooting silhouette competition and taking lots and lots of notes.

Powder sensitivities vary so POI will vary from powder to powder, that's why its important to take notes when at the range like temperature, wind speed and direction, himidity, altitude, etc.

This is how you will learn how your loads and rifles behave.

Now there are some tricks that help when shooting a match or practicing at the range when it's warmer. I keep my ammo on a small cooler with ice packs. This keeps the ammo cool and dry. However, as you shoot your chamber and barrel gets warmer and warmer so there might still be some change in your POI, again that why notes are so important.

Hope this helps and stay safe.

 

[Bravo 4]

Keep control of your ammo's temp in the summer, in other works don't let it heat up. Then just worry about the difference in environmentals between the two seasons, summer and fall. Then poi difference will probably only be a couple inches at that range, with about any modern cartridge. 500 yards seems like a long ways out, but it takes a substantial amount of environmental changes to amount to anything worth stressing over...especially if talking big game. The rifle's precision & shooter's accuracy potential or not shooting consistent ammo can/will play as much or more havoc on probability of a hit at that range than a swing in temp. Compound any of those factors together and you are going to start having problems. I usually just take some blue scotch tape and make a BDC turret off what my ballistic app says with what a middle temp for the day will be. That way you may be off a click or so (inch here and there) throughout the entire day, more than likely you can use this for an extended period of time...like a hunting season.