Deleted noremaximus
Good morning, could someone explain in simplest terms how I would use Air Pressure when reloading and shooting? Thank you.
Deleted noremaximus
outside air pressure.
Deleted noremaximus
Would the barometric pressure influence anything during the reloading process?
Deleted noremaximus
I guess my real question would be, how would I use barometric pressure? is it something I need to take into account when loading up ammo for a match, or is it something that needs to be taken into account when adjusting my scope, or hold over? thank you.
CharlieNC
Gold $$ Contributor
Not unless you get dizzy.
Now when shooting, the BP and temperature are the dominant variables affecting the bullet drop. There are many phone apps and JB Ballistics free on-line calculator which utilize these as inputs to determine the effects.
Deleted noremaximus
Okay, thank you Charlie.
Air pressure wouldn't change your reloading, but humidity could
if you went from a very dry to very moist atmosphere.
If has more of an effect on your bullets drop at distance.
As the others have said, get a ballistic app. and you can plug in
the changes to see how much it would effect your bullet at your
location and conditions.
Cold and a low elevations air is more dense than warm and a high elevation.
The denser air will be harder for a bullet to travel threw and cause more drop.
if you went from a very dry to very moist atmosphere.
If has more of an effect on your bullets drop at distance.
As the others have said, get a ballistic app. and you can plug in
the changes to see how much it would effect your bullet at your
location and conditions.
Cold and a low elevations air is more dense than warm and a high elevation.
The denser air will be harder for a bullet to travel threw and cause more drop.
100% correct. I might add also, if you’re engaging targets at a cosiderable distance say 1000 yds and out. Using station pressure could make the difference of a miss vs using a device properly calibrated to read the pressure of the location you are at when breaking the shot.
Ned Ludd
Silver $$ Contributor
One important consideration with respect to air pressure is that you want the tires of your vehicle inflated sufficiently to ensure that you make the trip to and from the range safely. 
For shooting, air pressure is part of the equation in terms of predicting bullet drop at some distance. Some use a calculation referred to as "Density Altitude" for that purpose. A more detailed explanation can be found here:
Although air pressure, as one part of the ambient environmental conditions that can affect external ballistics, can certainly affect trajectory, it is generally less important with regard to the reloading process. In other words, with respect to reloading, it's generally not a consideration. As long as you have worked up a load properly, you can travel to different elevations, which affects air pressure among other things, and the load will still shoot just fine. Obviously the affect of air pressure on external ballistics will have to be taken into account. In general, the higher the elevation, the less scope elevation will be require to center your shots at some specified distance with the same load. However, the effect of the typical changes in air pressure one might experience when shooting in different locations on internal ballistics are usually negligible. Velocity and tuning of a given load should remain relatively constant at different elevations, so the effect on external ballistics in terms of air density is far more important, as are other factors such as temperature and humidity. In general, most people will leave a tuned load alone when traveling to a location of markedly different elevation, merely noting the change in bullet drop predicted using a ballistics calculator for the new location as compared to the location where the load was developed. I can imagine there might be rare exceptions to this approach, but in general, if you cannot shoot the difference, there is no reason to change anything at the reloading level.
For shooting, air pressure is part of the equation in terms of predicting bullet drop at some distance. Some use a calculation referred to as "Density Altitude" for that purpose. A more detailed explanation can be found here:
Making Ballistic Cards Using Density Altitude
www.arcanamavens.com
Although air pressure, as one part of the ambient environmental conditions that can affect external ballistics, can certainly affect trajectory, it is generally less important with regard to the reloading process. In other words, with respect to reloading, it's generally not a consideration. As long as you have worked up a load properly, you can travel to different elevations, which affects air pressure among other things, and the load will still shoot just fine. Obviously the affect of air pressure on external ballistics will have to be taken into account. In general, the higher the elevation, the less scope elevation will be require to center your shots at some specified distance with the same load. However, the effect of the typical changes in air pressure one might experience when shooting in different locations on internal ballistics are usually negligible. Velocity and tuning of a given load should remain relatively constant at different elevations, so the effect on external ballistics in terms of air density is far more important, as are other factors such as temperature and humidity. In general, most people will leave a tuned load alone when traveling to a location of markedly different elevation, merely noting the change in bullet drop predicted using a ballistics calculator for the new location as compared to the location where the load was developed. I can imagine there might be rare exceptions to this approach, but in general, if you cannot shoot the difference, there is no reason to change anything at the reloading level.
Don't a few warm up shots account for drop? You don't need a computer.
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