Range Report Which is Most Important

[Jester8]

I was wondering the other day, out of the following which is most important, and why:

Air Temperature
Relative Humidity
Barometric Pressure
Altitude

I am wondering because, I shoot alot during the summer, then when hunting season comes around I want to know which one of these variables is the most important. Does any certain variable effect trajectory more than the other?

 

[Lindy]

Re: Which is Most Important

Well, humidity is least important. Air pressure and altitude are the same thing - air pressure declines at about 1 inch of mercury per thousand feet of altitude gain.

To see which is really more important to the kind of shooting you do, use a ballistic program. Vary one parameter at a time to see how much difference it makes. If you don't have one on your personal computer or PDA, use this:

JBM Ballistics

And don't overlook the fact that your muzzle velocity is also a function of temperature. How much depends on the powder.

 

[Jester8]

Re: Which is Most Important

Thanks for the tip Lindy. I have used JBM before, just never really played with it too much before. Guess I was looking for the short fast answer, but it will be more fun to play around with the program. Appreciate the help.

 

[1979Wolf]

Re: Which is Most Important

alt

 

[Short-bus]

Re: Which is Most Important

Pressure is the biggest, I played around with temperature changes, and they don't effect bullet trajectory quite as much as big changes in BP.

Branden

 

[runngun]

Re: Which is Most Important

The two real variables are air density, which affects the external ballistics, and temperature, which affects the internal ballistics (muzzle velocity)

Since humidity, temperature, elevation and weather all play a role in air density, it is much more useful to determine trajectory with respect to an idealized atmospheric model.

By using the density altitude for determining trajectory, you can correct for all the variables at the same time, instead of having to correct for each one individual.

If you have a way of calculating trajectory at the time of firing (PDA, iphone, etc) then you just plug and chug with the best avalible data.