So I've googled it. Still don't get it. I shoot just a few miles from a naval airfield (Blue angels training site) and can get hourly weather data on my phone. It gives temp, humidity, altitude pressure and millibars. So on my ballistic app it asks if the pressure is "absolute". Station pressure, absolute pressure, density altitude. So confusing. If the airfield is reporting 29.89 is that absolute or not. I don't have a Kestrel yet but it's on my list. And by the way my range is at sea level. NAF El Centro, Ca.
Help understanding baro pressure
- Thread starter mike a
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GSPV
A failure to plan is a plan for failure.
dmoran
Donovan Moran
Your range being at sea level, station pressure and barometric pressure would be equal !.!.!
Barometric pressure is actual air pressure corrected to sea level.
Station pressure is the actual air pressure at any location (not corrected).
Most ballistic programs use station pressure (actual air pressure).
Donovan
Barometric pressure is actual air pressure corrected to sea level.
Station pressure is the actual air pressure at any location (not corrected).
Most ballistic programs use station pressure (actual air pressure).
Donovan
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Easy solution - use a Kestrel.
So absolute pressure is station pressure which I need a Kestrel for. Right?
dmoran
Donovan Moran
@mike a
Not sure why your asking of absolute pressure? for its different and used for like scuba divers and gauge based atmosphere scenario's.
Your being so close to the air-base and at sea level, might as well take advantage of it, and get your needed air pressure data from your phone like you were thinking (I would...lol).
Donovan
Not sure why your asking of absolute pressure? for its different and used for like scuba divers and gauge based atmosphere scenario's.
Your being so close to the air-base and at sea level, might as well take advantage of it, and get your needed air pressure data from your phone like you were thinking (I would...lol).
Donovan
Last edited:
The reason I ask about absolute is because my ballistic (AE) asks if it is. I switched it back and forth may times and never saw a difference. Must be I'm at sea level (duh). I can buy a lot of bullets for the price of a Kestrel.
I believe that when they correct Barometric pressure, it is corrected to sea level. So, if you were at or close to sea level you would not see a difference. If you were at 6000 feet and sea level was at 30, you would see station pressure at around 24.00 Its about 1" of hg for every 1000 feet of elevation I think.
Pwdrjnkie
Gold $$ Contributor
The way i inderstand it, your phone "altitude pressure" is barometric pressure. The barometric pressure is the station (or absolute) pressure and your phone is correcting it for your elevation....only thing is, youre at sea level or 0 elevation, so both are the same. If you get a kestrel, it can tell you both...you just have to enter your elevation if you are asking the kestrel for barometric. And then, regarding bullet flight, density altitude and air temp are going to be most important. Density altitude value for how much atmospheric resistance is acting on the bullet and outside temp dictates your powder temp and therefore velocity changes. Hope that helps
This should help, since you're using data from a local airfield. http://www.pilotfriend.com/pilot_resources/density.htm
Regarding the above website, "Altimeter setting" is the barometric pressure reported at the station (air field). This number, when set into the aircrafts altimeter tells the pilot his pressure altitude above sea level, NOT above ground. This is important when landing at an airport such as Denver where the site altitude is 5433 ft above sea level, and an approaching aircraft must be at an altitude of 6433 ft (1000 ft above ground) to enter the landing pattern. Conversely, an aircraft landing at El Centro would only need 958 ft on the altimeter to commence landing, since the airport is at 42 ft BELOW sea level. (Note to the trolls, this is a deliberately simplistic explanation)
Pressure altitude (as reported at the airfield) is not the same as density altitude. The above website explains why this difference is important.
These four conditions combine to create thinner air ( a higher density altitude) , and therefore a flatter bullet trajectory.
Site altitude (above sea level)
Relative humidity (moisture in the air DECREASES air density)
Air temperature (hotter air is less dense)
Lowered Barometric pressure
The atmospheric "standard day" is 59 F, 29.92Hg, 50% relative humidity, at sea level.
For those new to the sport, this means that if shooting a bullet that is marginally stable for your caliber, it might shoot very well on a hot, humid, low pressure day at high altitude, but shoot terribly on a cold, dry, high pressure day at or below sea level.
My 9 twist 223 would only shoot the 75 grain HPBT when the temp was above 100 F on a typical humid day here in central Texas. If the temperature was lower, and the air drier, it shot like crap. Didn't matter if it was my hand load, or off the shelf Superformance load.
Regarding the above website, "Altimeter setting" is the barometric pressure reported at the station (air field). This number, when set into the aircrafts altimeter tells the pilot his pressure altitude above sea level, NOT above ground. This is important when landing at an airport such as Denver where the site altitude is 5433 ft above sea level, and an approaching aircraft must be at an altitude of 6433 ft (1000 ft above ground) to enter the landing pattern. Conversely, an aircraft landing at El Centro would only need 958 ft on the altimeter to commence landing, since the airport is at 42 ft BELOW sea level. (Note to the trolls, this is a deliberately simplistic explanation)
Pressure altitude (as reported at the airfield) is not the same as density altitude. The above website explains why this difference is important.
These four conditions combine to create thinner air ( a higher density altitude) , and therefore a flatter bullet trajectory.
Site altitude (above sea level)
Relative humidity (moisture in the air DECREASES air density)
Air temperature (hotter air is less dense)
Lowered Barometric pressure
The atmospheric "standard day" is 59 F, 29.92Hg, 50% relative humidity, at sea level.
For those new to the sport, this means that if shooting a bullet that is marginally stable for your caliber, it might shoot very well on a hot, humid, low pressure day at high altitude, but shoot terribly on a cold, dry, high pressure day at or below sea level.
My 9 twist 223 would only shoot the 75 grain HPBT when the temp was above 100 F on a typical humid day here in central Texas. If the temperature was lower, and the air drier, it shot like crap. Didn't matter if it was my hand load, or off the shelf Superformance load.
Ha. Yep. My 22-250 1-14 twist shoots the 53 gr v-max decent at 6000 feet and keyholes at 1000 feet
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