Barrel temperature

[Koda]

I'm over my head on this but I will ask in prose and see what discussion we get, correct me if I'm wrong. My main hunting rifle has a thin factory barrel that heats fast, and im beginning to track POI change but there are so many variables... all other variables equal except air temp the day you shoot. So it made me wonder....

Assume a cold bore zero... Is the POI change from barrel temp rising delayed the lower the outside ambient temperature is?

based on observations, if I'm shooting on a hot summer day the temp changes faster than on a cold winter day, so if the temp change is delayed due to colder air temp then would it be logical to say the POI change is less dramatic on cold days as it is on hot days? In other words, could you get one more shot at the cold bore zero POI?

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[Flopsweat]

Does it really change so much that a precise "cold barrel" and rough "hot barrel" POA aren't enough for hunting?

 

[bionic knees]

I'm over my head on this but I will ask in prose and see what discussion we get, correct me if I'm wrong. My main hunting rifle has a thin factory barrel that heats fast, and im beginning to track POI change but there are so many variables... all other variables equal except air temp the day you shoot. So it made me wonder....

Assume a cold bore zero... Is the POI change from barrel temp rising delayed the lower the outside ambient temperature is?

based on observations, if I'm shooting on a hot summer day the temp changes faster than on a cold winter day, so if the temp change is delayed due to colder air temp then would it be logical to say the POI change is less dramatic on cold days as it is on hot days? In other words, could you get one more shot at the cold bore zero POI?

one-shot, one kill, no worries.

 

[Greenbug]

What are you hunting that requires multiple shots?
Are we talking about a varmint rifle for sage rats or prairie dogs?

 

[Koda]

Does it really change so much that a precise "cold barrel" and rough "hot barrel" POA aren't enough for hunting?

Probably not, I dont have enough data yet to say how far ive noticed about 3rds it starts to climb and the barrel is getting warm enough to touch.

 

[Koda]

one-shot, one kill, no worries.

typically yes, but I just want to know for the worst case and general target shooting.

 

[Koda]

What are you hunting that requires multiple shots?
Are we talking about a varmint rifle for sage rats or prairie dogs?

big game, I dont need multiple shots but just curious about target shooting and learning.

 

[Nosferatu]

If you're second shot is 6-8" out of your first, you have a problem. Anything inside that is fine. You don't need sub-MOA shot-to-shot for big game hunting.

 

[Ura-Ki]

Your on the right track with this!
Several things are happening to your rifle in the field, The Ambient temp will be your "Cold Bore" and all else being equal, should align POI/POA with how you zeroed it. As temps go up, the metal expands slightly ( VERY SLIGHTLY) and velocities can increase, ( Slightly) mostly due to the air temps and even altitude! As the barrel heats up through additional shots, it's going to loosen up even more, this time noticeable, this is why you see its groups opening up some, even sending flyers! the opposite happens in very cold temps, the barrel will hold POI/POA longer, but may shift the cold bore results a little! As bad as that is, your ammo is even more sensitive, cold temps can make your ammo "Lazy" partly due to the slower burn ( Getting up to temp in the chamber) and denser air which is thicker! In high heat, and especially at higher altitudes ( Density Altitude) the shots can pick up a couple hundred feet per second, and that can also change the POI/POA signiffigently! his is why you see marksmen setting their ammo out in the sun to heat it up as it can both increase the effective range, and velocities! The heavier the barrel contour, the more mass that any heat must overcome or equalize, and that's why you see varmint rifles, and even some big mage rifles wearing bull barrels! We used to have to "Math it out" in the service to determine if there would be any changes and through experience with the rifle, generally knew what changes to expect and what dope to hold or dial in! Pretty cool stuff to witness, especially when the air density is way up and there is lots of humidity, you can actually see the bullet's track as its shock wave pushes the vapers out of the air and makes the visible swirl!

 

[Koda]

There seems to be a distraction over hunting.... I half wish I didn't mention this was a hunting rifle, it just happens to be what I have. I'm more concerned about learning the effects of temperature so I can apply that to whatever application I need.
I'm fine with my hunting marksmanship and whats acceptable for "minute of deer", that's not what my question is about...

That said, I am working on applying for a pronghorn tag which is in the heat of summer where I have noticed a larger POI change on very hot days. The last time I hunted pronghorn it was in 100 degree weather no shade. With my pencil thin barrel at long ranges I do wonder if my POI could change enough to matter on a second or third shot.

 

[P7M13]

Also depends a lot on the residual stress in your barrel.
Heat effects on your barrel is a function of the barrel material thermal conductivity, the steel's coefficient of emissivity, and the surface delta-T.
In short, 1, 2 or 3 shots in close Tim to one another, likely minimal change in POI.
Edit, the mirage from the heat off your barrel likely has a significant effect on your shot to shot accuracy.

 

[Ura-Ki]

There seems to be a distraction over hunting.... I half wish I didn't mention this was a hunting rifle, it just happens to be what I have. I'm more concerned about learning the effects of temperature so I can apply that to whatever application I need.
I'm fine with my hunting marksmanship and whats acceptable for "minute of deer", that's not what my question is about...

That said, I am working on applying for a pronghorn tag which is in the heat of summer where I have noticed a larger POI change on very hot days. The last time I hunted pronghorn it was in 100 degree weather no shade. With my pencil thin barrel at long ranges I do wonder if my POI could change enough to matter on a second or third shot.

Short answer, on a cold bore, NO, but consecutive following shots will change POI enough to be an issue! Only way to find out what that may end up looking like is to replicate those shots and observe the shots! Don't forget that shooting up hill will also effect the POI/POA, more then a down hill shot, and then there is always the wind, and that can play an even bigger role on your results! Unless you have a very high BC that can really buck the wind, you got your work cut out for you!

 

[Koda]

Your on the right track with this!
Several things are happening to your rifle in the field, The Ambient temp will be your "Cold Bore" and all else being equal, should align POI/POA with how you zeroed it. As temps go up, the metal expands slightly ( VERY SLIGHTLY) and velocities can increase, ( Slightly) mostly due to the air temps and even altitude! As the barrel heats up through additional shots, it's going to loosen up even more, this time noticeable, this is why you see its groups opening up some, even sending flyers! the opposite happens in very cold temps, the barrel will hold POI/POA longer, but may shift the cold bore results a little! As bad as that is, your ammo is even more sensitive, cold temps can make your ammo "Lazy" partly due to the slower burn ( Getting up to temp in the chamber) and denser air which is thicker! In high heat, and especially at higher altitudes ( Density Altitude) the shots can pick up a couple hundred feet per second, and that can also change the POI/POA signiffigently! his is why you see marksmen setting their ammo out in the sun to heat it up as it can both increase the effective range, and velocities! The heavier the barrel contour, the more mass that any heat must overcome or equalize, and that's why you see varmint rifles, and even some big mage rifles wearing bull barrels! We used to have to "Math it out" in the service to determine if there would be any changes and through experience with the rifle, generally knew what changes to expect and what dope to hold or dial in! Pretty cool stuff to witness, especially when the air density is way up and there is lots of humidity, you can actually see the bullet's track as its shock wave pushes the vapers out of the air and makes the visible swirl!

love this answer, thank you it helps. This is what Im looking for .

I didnt know it could even cause fliers, and I may have experienced that last summer which helps me know not to chase that zero. I think its good news that the cold takes longer to affect POI since most hunting is late fall.

 

[Koda]

Also depends a lot on the residual stress in your barrel.
Heat effects on your barrel is a function of the barrel material thermal conductivity, the steel's coefficient of emissivity, and the surface delta-T.
In short, 1, 2 or 3 shots in close Tim to one another, likely minimal change in POI.

now Im over my head but if I read that correctly this might explain different results based on how quickly followup shots are made. Basically the time it takes for the heat to affect the barrel metal?

 

[Koda]

Don't forget that shooting up hill will also effect the POI/POA, more then a down hill shot,

Will the angle affect the grouping size or are you talking about affecting holdover?

 

[Ura-Ki]

Will the angle affect the grouping size or are you talking about affecting holdover?

I would take your rifle out with the planned hunting ammo and observe it's performance and note the changes in your "Hold" for your angles
All things being equal, the groups should stay the same, but your hold will not! Usually you need to hold over an extra 1/4 to 1/3 MOA, but that all depends on Caliber, Velocity and BC!

 

[Koda]

I would take your rifle out with the planned hunting ammo and observe it's performance and note the changes in your "Hold" for your angles
All things being equal, the groups should stay the same, but your hold will not! Usually you need to hold over an extra 1/4 to 1/3 MOA, but that all depends on Caliber, Velocity and BC!

I actually plan to do that, but for now Ive heard that if you hold over for the horizontal distance only it doesnt matter if your shooting up or down hill. Is that correct? Note, I use a laser range finder set to compensate for angle, it just gives the true horizontal range.

 

[Ura-Ki]

I actually plan to do that, but for now Ive heard that if you hold over for the horizontal distance only it doesnt matter if your shooting up or down hill. Is that correct? Note, I use a laser range finder set to compensate for angle, it just gives the true horizontal range.

Down hill, you have to hold ( Slightly) short, up hill, you have to hold over, and that can actually be quite a lot!

 

[Greenbug]

Down hill, you have to hold ( Slightly) short, up hill, you have to hold over, and that can actually be quite a lot!

Explain to us how the effect of gravity changes depending on if your barrel is pointed uphill or downhill.

This should be good.

 

[Nosferatu]

Explain to us how the effect of gravity changes depending on if your barrel is pointed uphill or downhill.

This should be good.

It's not just gravity, but the arc of the bullet path after it leaves the barrel.

Archery hunters learn this quickly when you sail an arrow aver a deer because you held too high on a downhill slope.