Mirage from barrel - POI

[CA_Shooter]

I searched prior to posting this and could not get a definitive answer.

Also, I have a mirage shade that I'm going to start using.

That said, when NOT using a mirage shade, when the barrel gets hot AND using a scope, how does this distort the POI?

Do shots go high or low? I've found that my POI lowers as the barrel gets hot. Does mirage from barrel heat lower or raise POI?

 

[TylerFromMS]

They’ve always hit a lower POI for me. I occasionally blow down the barrel to move it. A mirage shield would be a better solution I think.

 

[miles13]

Set a fan on the bench and blow the mirage away.

 

[TylerFromMS]

Set a fan on the bench and blow the mirage away.

I don’t know if they’re technically legal in F. Not sure at all, honestly. The DeWalt battery one is awesome.

 

[miles13]

I don’t know if they’re technically legal in F. Not sure at all, honestly. The DeWalt battery one is awesome.

I use my Milwaukee on the bench, it's way better than the Dewalt.

 

[TylerFromMS]

I use my Milwaukee on the bench, it's way better than the Dewalt.

I’m poor. Harbor Freight if I got one.

 

[Ned Ludd]

...That said, when NOT using a mirage shade, when the barrel gets hot AND using a scope, how does this distort the POI?...

The term "mirage" refers to convection currents in the air caused by thermal variation. Warm air and colder air have different densities, and thus transmit and refract light differently. The rifle scope is sitting right on top of a very good air heater (barrel) and looks over it longitudinally, so the depth of the field distortion due to the heated air rising from the barrel can be significant. In fact, when shooting a long string of fire, the mirage from a long barrel can get so bad it can make it almost impossible to even see the target. A mirage shade simply diverts most of the heated air from the hot barrel off to either side, away from being directly in front of the scope objective. A mirage shield has no effect on mirage that occurs in the air between the shooter and the target.

 

[CA_Shooter]

They’ve always hit a lower POI for me. I occasionally blow down the barrel to move it. A mirage shield would be a better solution I think.

The term "mirage" refers to convection currents in the air caused by thermal variation. Warm air and colder air have different densities, and thus transmit and refract light differently. The rifle scope is sitting right on top of a very good air heater (barrel) and looks over it longitudinally, so the depth of the field distortion due to the heated air rising from the barrel can be significant. In fact, when shooting a long string of fire, the mirage from a long barrel can get so bad it can make it almost impossible to even see the target. A mirage shade simply diverts most of the heated air from the hot barrel off to either side, away from being directly in front of the scope objective. A mirage shield has no effect on mirage that occurs in the air between the shooter and the target.

Tyler has noticed that mirage from the barrel causes the POI to go low. This is what I have noticed also.

Does anyone have any reasoning on why it's specifically lower? Or is it just coincidental that we both think it's causing a lower POI?

 

[TylerFromMS]

Tyler has noticed that mirage from the barrel causes the POI to go low. This is what I have noticed also.

Does anyone have any reasoning on why it's specifically lower? Or is it just coincidental that we both think it's causing a lower POI?

South Texas Marksmanship Training Center - Reading Mirage

 

[Joseph Cordeiro]

You should use a mirage shield at all times whether or not it is hot or cold outside. 2 reasons. One the mirage shield minimizes heat mirage produced by the hot barrel. Two the mirage shield can change the harmonics on the barrel which will in turn change point of impact.

 

[CA_Shooter]

South Texas Marksmanship Training Center - Reading Mirage

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

You should use a mirage shield at all times whether or not it is hot or cold outside. 2 reasons. One the mirage shield minimizes heat mirage produced by the hot barrel. Two the mirage shield can change the harmonics on the barrel which will in turn change point of impact.

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

 

[JMayo]

Mirage effects my ability to aim = poa
I use a shield and a small fan.

The rifle barrel getting hot makes my bullets track up & R = poi,
when keeping same poa.

Bench Rest

 

[TylerFromMS]

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

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.

 

[gunsandgunsmithing]

Sometime when mirage is pretty bad, leave the rifle in the rest, warm barrel or not, and just watch through the scope without touching the rifle. Watch the reticle dance against the target. What you see is relative to POI. Point being, you may "see" the target as being high, low, left or right at different times. If you see it as being high and you hold on the "dot", you'll shoot high. The light is bending and the way we see the target is changing with it. Look at it this way...you're hitting what you're seeing but what you're seeing is lying to your eyes. In a perfect world, we wouldn't miss by more than the mirage displaces the image we "see." In the real world, the wind currents and varying densities affect the direction of the mirage and that may well displace the bullet further than the mirage/image alone.

 

[gunsandgunsmithing]

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, shoot 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

I can't agree with the logic. If I see the target higher than it is, and I aim higher due to that, how am I going to shoot low?

 

[TylerFromMS]

I can't agree with the logic. If I see the target higher than it is, and I aim higher due to that, how am I going to shoot low?

No, that's what he was saying. If you cheat high, then the poi will be the same as when there was no boil. If you don't hold half a ring high, then the shot will go low. Words are hard for me sometimes.

I edited the other post to say "hold" half a ring high rather than "shoot".

Also, I need another tuner.

 

[gunsandgunsmithing]

No, that's what he was saying. If you cheat high, then the poi will be the same as when there was no boil. If you don't hold half a ring high, then the shot will go low. Words are hard for me sometimes.

I edited the other post to say "hold" half a ring high rather than "shoot".

Also, I need another tuner.

I'll concede that I may be wrong but I fail to see the logic, yet. What If the mirage is running left to right? Do I hold MORE to the right? I can't see that either, but of course, wind is at play if it's running sideways, too.

I do see mirage as being a wind that you can see and I try to hold accordingly.

 

[TylerFromMS]

I'll concede that I may be wrong but I fail to see the logic, yet. What If the mirage is running left to right? Do I hold MORE to the right? I can't see that either, but of course, wind is at play if it's running sideways, too.

I do see mirage as being a wind that you can see and I try to hold accordingly.

Mirage running left to right represents actual wind for me. Mirage rising straight up generally is the lack of wind, that is, a boil. The boil displaces the target for me, whereas the left to right doesn't displace the target, but is an indicator of a wind condition between me and the target. The boil always rises, think of asphalt in the summer... "monkeys dancing". Dunno. It works for me.

 

[CA_Shooter]

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

Thank you for the description and excellent image example, and this is where I am confused.

If mirage is moving up and it makes the shooter think the target is higher than it is, wouldn't that make the POI go higher on the target instead of lower on the target?

I mocked up the image you sent.

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

So on the actual target, the green circle, the hits are high. Not low

 

[newbieshooter]

Mirage off the barrel is floating up. The target looks like it's higher than it actually is, so shots go low.......

View attachment 1229776

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


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)?