Mirage from barrel - POI

[TylerFromMS]

Dunno. I'm just sharing my experience and theories. It works for me. It might not for you. It's kind of like the "sun's up, sights up" thing to me. It might be witchcraft for all I know. I do know that when my barrel gets hot, if I don't blow over the top of it right before I shoot, it'll be low.

 

[CA_Shooter]

Dunno. I'm just sharing my experience and theories. It works for me. It might not for you. It's kind of like the "sun's up, sights up" thing to me. It might be witchcraft for all I know. I do know that when my barrel gets hot, if I don't blow over the top of it right before I shoot, it'll be low.

I have the same experience and am wondering why it happens. Because it seems as though heat acts differently when under the scope vs at the object being looked at

 

[CA_Shooter]

Ok, so I did the following experiment at home.

I used an FFP scope and an electric stove top.

On the stove, with the end of the scope right under one of the heating plates, I aimed the reticle at a telephone pole device.

After being comfortable where it was aimed, I turned the stove up all the way to create heat under the scope. I noticed the target (telephone pole device) seemed to drop

I then let the stove completely cool, and again verified through the scope that the telephone pole went back up again into its original position when heat was not applied.

RESULT: it turns out that the target dropped when I turned up the heat. So this would follow that heat rising from under the scope would cause shots to hit low on the target.

I have attached a diagram to explain what I found. The black lines represent the telephone line device

Anybody know why? Is this like how in some mirrors you look upside down?

 

[Robert G]

I can only add that when shooting through iron sights at distance, we as BPTR shooters often try to avoid shooting in a boil because our shots will almost always go high. I can't imagine why that would be different in a scope. Obviously if you're doing something different and it's working then keep doing it.

 

[Lbart]

Ok, so I did the following experiment at home.
I used an FFP scope and an electric stove top.
On the stove, with the end of the scope right under one of the heating plates, I aimed the reticle at a telephone pole device.
After being comfortable where it was aimed, I turned the stove up all the way to create heat under the scope. I noticed the target (telephone pole device) seemed to drop
I then let the stove completely cool, and again verified through the scope that the telephone pole went back up again into its original position when heat was not applied.
RESULT: it turns out that the target dropped when I turned up the heat. So this would follow that heat rising from under the scope would cause shots to hit low on the target.
I have attached a diagram to explain what I found. The black lines represent the telephone line device
Anybody know why? Is this like how in some mirrors you look upside down?

If the scope gets hotter it will tend to get bigger & because of that move the crosshair higher causing the target image to appear lower. If the air/mirage only gets heated the opposite will occur.

 

[CA_Shooter]

If the scope gets hotter it will tend to get bigger & because of that move the crosshair higher causing the target image to appear lower. If the air/mirage only gets heated the opposite will occur.

Oh wow that is very interesting! How hot would the barrel need to get to have that heat move up to the scope to heat it and make the cross hair higher? And would a mirage shield be sufficient to prevent heating the scope?

 

[rardoin]

S

Oh wow that is very interesting! How hot would the barrel need to get to have that heat move up to the scope to heat it and make the cross hair higher? And would a mirage shield be sufficient to prevent heating the scope?

Sunlight would be heating the optics.

 

[shoot4fun]

I have thought that any change in POI from mirage is due to the fact that mirage will affect your POA.
I also would think that, as mirage is heat, that heat could/would cause a shift in POI and not the mirage.
But I'm just a hick from Alabama .

 

[Straightshooter1]

To me, it's simple physics for the refraction of light. It's really no different than the mirages we see on a hot highway or on a vast expanse of desert . . . or over a long shooting range on a hot day. The refraction from across the heat boundary makes an image appear lower, so your POA/target will actually appear lower to you than it is because of that refraction. And, I imagine that if one has enough heat coming off a barrel where you have a boundary between the heated air the cooler air, that too would create some refraction over the barrel.

 

[Joseph Cordeiro]

Didn't see anything about how rising heat right at the scope from the barrel would impact POI. Appreciate the link, really good insight on reading mirage



Totally. I will be doing this going forward. Luckily my mirage shield only touches my handguard so it won't impact harmonics

You can also lower your scope magnification until it clears up your target view with heavy mirage.

 

[JFrank]

I still don't get it..."...target looks like it's higher than it actually is"........

View attachment 1229790
Assume shooter is zero'ed at the true position of the target prior to any mirage.

Let's exaggerate here for a moment. if the mirage off the barrel is so bad...that the displacement as displayed in the diagram is 5 feet - so the position of the target as seen by the shooter is 5 feet above the actual target - and you aim at the perceived target (cause that's where you think the target is). Now you are aiming 5 feet above the actual target. How can your shot be lower than the true position of the target (which is 5 feet below where you were aiming)?

So if the mirage from barrel heat is bad enough do we just keep aiming higher?

 

[D-4297]

Not necessarily . Shoot at Ben Avery in say mid - July , when ambient is 105 - 109F at 10:30 a.m. , but actual ground temp is 130F or higher , at 600 yard line . You can have mirage that can make your target turn into a complete blur at , lets say 30x . Turn it all the way down , and you now have a barely "useable target picture" . If your rifle sits on the line uncovered for ten minutes before you shoot , what has happened to the optics inside the scope ,, plus now you will be adding "barrel mirage" into the equation . When I see this occur , I usually place my "Dot" at the bottom of the X-ring . I do get a lot of ten's and X's this way . And a few 9's , too . You have multiple mirage issues working against each other , and reading mirage is sometimes more difficult than trying to read wind . Takes practice , and understanding what's causing what .

 

[foxguy]

Ok, just trying to understand this a little better.

So you are asking specifically about mirage off of a hot barrel. So its cool enough outside and no mirage is coming off the range. This may warrant further discussion??

Smoketheclay

Viewing your image, your point of aim is high due to mirage on the range floating the target image above the actual target. Thus causing a high point of impact on the actual target.

•Green circle is the actual target.
•red dot is the aim point on the mirage circle and the POI

 

[Longtrain]

Once early on in LR shooting, I was pounding the X ring, figuring this was a walk in the park. All of a sudden I started shooting high 8’s, one after another with a good center target hold. A seasoned shooter who was watching my target said, “how do you like shooting in a boil?” The worse mirage is when your target has no visible rings, isn’t round and dances all over your sight picture.

As far as mirage off the barrel, it really distorts the target, assuming the target is clear. Trying to focus to a select the area of the target you are aiming at is difficult. slight wind will push it side to side. If the wind is up a bit, I don’t see the barrel mirage. But combine barrel mirage with target mirage and you’re shootings in a bucket of pea soup.
Don’t forget your mirage shield.

 

[Rat Rifle]

Which is best to prevent barrel mirage, a shield, a fan, or both ?

 

[ED3]

Mirage off the barrel is floating up. The target looks like it's higher than it actually is, so shots go low. It's like shooting in a boil, only it's right in your face instead of at range. A guy I shoot with that is a really good shooter and teacher said "try this: when it's boiling, hold a half a ring high and see where it lands". It works, at least at 600, so that's where my conclusion came from.

View attachment 1229776

That is contrary to what is implied in the text accompanying that illustration in its original context:

"... A boiling mirage is present when there is no measurable wind, and when the wind blowing from the shooter directly toward the target (6 o’clock wind) or from the target toward the shooter (12 o’clock wind). This mirage class condition requires that the rear sight be lowered, to center the shot group within the target. ..."

 

[gunsandgunsmithing]

Which is best to prevent barrel mirage, a shield, a fan, or both ?

No question...BOTH! If I had to pick one, it'd be the fan.

 

[CA_Shooter]

Ok, just trying to understand this a little better.

So you are asking specifically about mirage off of a hot barrel. So its cool enough outside and no mirage is coming off the range. This may warrant further discussion??

Smoketheclay

Viewing your image, your point of aim is high due to mirage on the range floating the target image above the actual target. Thus causing a high point of impact on the actual target.

•Green circle is the actual target.
•red dot is the aim point on the mirage circle and the POI

View attachment 1230362

My original question was specifically for barrel heat mirage, and really nothing else. Imagine down at the target there isn't mirage. Just mirage from the barrel heat