by Jeff Johnston - Tuesday, June 7, 2011
True or False: You should aimhigher in rain and/or dense fog because humidity increases air resistance.
The Expert Deferral: "The Bullshooter’s Bible" (aka, the NRA Firearms Fact Book) says:
"Many target shooters have noticed that bullets seem to impact higher on the target when fired in rainy conditions. Changes in humidity have little effect on the air density, and thus on the flight of the bullet. Changes in barometric pressure, on the other hand, do have an effect. In general, fair weather in accompanied by a high barometer, which means more air density and more resistance to the bullet. Likewise, rainy weather is likely to occur at times of low barometer, when air pressure is low, producing less air density and resistance to the bullet. A drop of 1” in the barometric reading will increase the ballistic coefficient by about 3 1/3 percent."
The Second Opinion: While numbers don't lie, several retired Navy SEALS have been operating a long range shootingschool for hunters, called the Sportsmans All Weather, All Terrain (SAAM) course that's offered atTexas' FTWranch. The SEALSconfirm that humidity occurs in times of LOW pressure and does not effect bullets like high barometric pressure does.However, after 600 students and several tours in the desert, they have also learned some practical lessons; afterall, that's what the class is all about. And one of those is: For hunting ranges, shots inside of 600 yards or so, the hunter shouldn't worryabout compensatingfor air pressure.
Conclusion: False. In fact, it's the opposite, but hunters shouldn't ever worry about rain. And If you don’t believe the Fact Book, believe our Navy SEALs.
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