Barrel mirage

Um, why does that guy have a venetian blind stuck to his barrel?

This article is about how the mirage effect can affect shooting performance. For those of you who may want more in-depth information on the optical phenomenon itself, Wikipedia has an article for that. (I know; what are the odds?)

A barrel mirage is an optical illusion created as heat radiates from a rifle barrel and rises upwards in waves, "cooking" and distorting the air immediately above the barrel and refracting the shooter's view of the target.

As the barrel of a rifle gets hot from repeated firing, the heat from the will barrel rise, effectively cooking and distorting the air directly in front of the scope's front lens. In other words, the rifle creates its own miniature mirage, in what is probably the worst place possible — smack-dab in the shooter's line of sight — which can literally move your apparent point of aim on the target relative to your cross-hairs, causing you to miss the shot.

The specific effect on a shooter's accuracy as a result of this will vary according to local conditions but they can be more than enough to ruin a score, especially in events such as 300m free rifle competitions, where a fraction of a minute of angle can decide an entire match. "Local conditions" can be such things as temperature, barometric pressure, humidity, and more. While wind is normally not your friend on a shooting range, it will actually dissipate the heated air above your barrel, reducing or even eliminating the mirage effect.

Mirage shields

Different shapes give different distribution patterns of heat.

In order to deal with this bothersome phenomenon, someone^who? came up with the idea of using a strip of material to redirect the heated (distorted) air away from the shooter's line of sight, allowing a shooter to hit their targets more reliably. The exact effect of a shield will depend on both its width and curvature, if it has any. While flat shields were the standard for decades, recent years have seen more and more shooters opt for a curved strip, with the edges curving upward.

Bench rest shooters have been using barrel shields for decades but it has only been in recent years that other disciplines such as varminters, which have traditionally ignored them, have begun adopting them on a wider scale.

Although tactical shooters should use mirage shields for long-distance/slow-fire stages, for the most part, they don't bother. But although mirage shields can detach if you're crawling around in the bush, for many tactical shooting situations, a mirage shield is both practical and recommended.

	Varminters should use mirage shields. Think about it. You've invested thousands of dollars in a fancy varmint rifle and quality scope. You may have spent hundreds of dollars traveling to the varmint fields and spent dozens of hours loading up your ammo. Without a mirage shield on your barrel, once that barrel gets hot, you WILL get mirage effects that can make you miss a shot.
— Boyd Allen

So, yes, you do need a mirage shield to shoot at your best accuracy when the barrel gets hot. You can make your own shield from a scrap blind or, if you can't be bothered with making your own, purchase a ready-made plastic or aluminum shield. Sinclair International, Shotmaster 10X, and numerous other companies offer these in a wide variety of styles for a small price.