Effect of Mirage on Point of Impact

NMC_EXP · Post by **NMC_EXP** » Thu Jul 05, 2012 7:48 pm

I am fairly new to small bore. I primarily shoot (US) conventional outdoor prone. This week I shot when the air temperature was 97 deg F. The mirage was the heaviest I've ever seen. It was severe enough I could not see shot holes at 100 yards with my spotting scope and the bull was heavily distorted.

Wind was 5 to 10 MPH and swinging from 8:00 to 4:00. At this stage I am concentrating on doping wind speed and direction and have made no attempt to compensate for the effect of mirage on point of impact.

The mirage was changing from L to R, R to L and boiling at times.

Questions:

1. If the mirage is running left to right and leaning at a 45 degree angle, is the apparent location of the bull shifted high and right, in other words the image is being carried in the direction the mirage is running?

2. If a person is compensating properly for wind speed and direction, how far can shots be displaced by the effect of heavy mirage?

Thanks

Jim

Rover · Post by **Rover** » Thu Jul 05, 2012 10:10 pm

I'm not sure I can tell you what you want to know.

Back in the day, when I used to shoot Benchrest, many times I saw the target move completely off the crosshairs from the mirage. We were shooting for group and not score, so it didn't matter. What was important was that the mirage was running the same each time we fired.

It was about this time that the practice of "machine gunning" was developed; shooting five shots as fast as you could before the condition changed.

I don't know if you can apply any this to your shooting, but Good Luck!

NMC_EXP · Post by **NMC_EXP** » Fri Jul 06, 2012 5:51 am

Rover

Im the past I shot a lot of highpower. While shooting 600 yard prone I have seen the bullseye drift away from the front sight due to mirage.

Regards

Jim

RossM · Post by **RossM** » Sat Jul 07, 2012 11:24 pm

You might like to check out this download on wind shooting. Includes notes on mirage as well. Good shooting.

viewtopic.php?t=33868&highlight=

Go down to my post RossM on page 1.

NMC_EXP · Post by **NMC_EXP** » Wed Jul 11, 2012 9:02 pm

RossM

Thanks for the link. I've saved the article.

Regards

Jim

Bill Burkert · Post by **Bill Burkert** » Mon Jul 16, 2012 3:46 pm

Your best bet when shooting with mirage present is to use it to your advantage. Simply pick a condition, hopefully the most prevalent, and shoot in it.

For example, if it is running left to right and that is the condition in which you shooting, then do not shoot if the mirage starts to boil straight up or runs the other way.

Use your sighter, not your record bull, to see the effect of the new condition. The best prone shooters make use of their sighter even after going for record.

Keith Lay · Post by **Keith Lay** » Tue Jul 17, 2012 2:56 pm

Jim, these are a couple of questions I think I can answer for you. The answer to question #1 is definitely yes and question #2 is up to 2 moa(roughly 2 inches @100yds). I shoot blackpowder rifles(not muzzleloaders but cartridge rifles) competitively at mid-range to long range distances and small bore follows alot of the same principles. We do all of our shooting outdoors and reading mirage is a large part of our game. If you're not a good mirage reader you'll be at the bottom of the food chain in short order in our events. Question #2 is also affected a bit by rate of twist of the barrel and whether it is a right or left twist but 2 moa will usually get you in the ballpark. Agree with the posters above, try to shoot in similar conditions if possible if the wind is cycling. When the condition/mirage is rapidly changing and the clock is running we have to do a bit of seat-of-the-pants guessing however.
BTW, most of my trigger time is done with an Anschutz 8002 standing and I do alot of lurking here and usually don't have alot of anything meaningful to add for you guys but think I can help here lol. This gun is great practice for the most difficult portion of our events-offhand shooting at 200yd to 200m.
Keith Lay

NMC_EXP · Post by **NMC_EXP** » Wed Jul 18, 2012 10:39 am

Bill

Thanks for the input. I agree regarding shooting in the prevalent condition as indicated by the mirage. My question about the amount of displacement that mirage can cause was academic - I was not planning to "shade" the mirage.

Regards

Jim