Effects of altitude on power factor?

[Rich406]

I’ve been working up some loads for next year, and I got to thinking about the effect of altitude on power factor. I live at 5500 feet and I will shoot atleast one major match at sea level next year. 

 

I usually load to 133-135 PF. I assume that I will lose some PF at sea level, but how much? Does anyone have any first hand experience with this? I searched around but didn’t find a definitive answer...

[Jakobi]

I live and load at ~4000 ft and have not noticed a difference in power factor when I go up or down in elevation. At distance (several hundred yards) relative air density matters but not at 10 feet.

Edited December 23, 2018 by Jakobi

[drewbeck]

+1, temperature is usually only factor that we have to deal with for internal ballistics (depending on powder) at the chrono.

 

External ballistics doesn’t  play much of a role in Uspsa but at long ranges the affect of temp and barometric pressure are the biggest factors that come in to play after gravity, wind, and inclination, with regards to external  ballistics affecting bullet flight and velocity.

[Rich406]

Thanks for the info, one less thing to worry about.  

[Jfitz427]

On 12/23/2018 at 12:18 AM, drewbeck said:

+1, temperature is usually only factor that we have to deal with for internal ballistics (depending on powder) at the chrono.

 

External ballistics doesn’t  play much of a role in Uspsa but at long ranges the affect of temp and barometric pressure are the biggest factors that come in to play after gravity, wind, and inclination, with regards to external  ballistics affecting bullet flight and velocity.

I’m not sure tempature is the only factor. When I look at my 9 major load, I’m a full grain less then some people in different parts of the country. I’ll be loading say 7.3 for a 124 and they’ll be using 8.3+ for same power factor. I’m in Nc, and it’s hot, but it’s just as hot in Arizona, Nevada, Texas etc. all over the country the loads seem to vary a lot, but Pf is the same. If I was shooting minor, I’d probably set my loads up to be a good 10pf+ more then minor just to be safe. Still super soft shooting.  

[drewbeck]

I’m not sure tempature is the only factor. When I look at my 9 major load, I’m a full grain less then some people in different parts of the country. I’ll be loading say 7.3 for a 124 and they’ll be using 8.3+ for same power factor. I’m in Nc, and it’s hot, but it’s just as hot in Arizona, Nevada, Texas etc. all over the country the loads seem to vary a lot, but Pf is the same. If I was shooting minor, I’d probably set my loads up to be a good 10pf+ more then minor just to be safe. Still super soft shooting.  

The barrel and overall length/internal capacity are going to be the reasons why you’d experience what your describing. For example I have two 5” KKM barrels that run 5-6 pf different with the exact same batch of ammo.

Powder lots will also contribute to variations in pf but are generally less than barrel influences in my experience.


Sent from my iPhone using Tapatalk

[RePete]

Altitude does have an affect, but not too much if you are not running on the PF line.  The bigger problem will be humidity.

 

I DQ'd a shooter for a PF of 162000PF instead of the 168000PF that he run 2 weeks earlier.  All loaded at the same time.  The coditions were 2 weeks earlier the humidity was about 40%, and the rainstorm that went through the day before he shot raised the humidity to 95%.

[GrumpyOne]

58 minutes ago, RePete said:

Altitude does have an affect, but not too much if you are not running on the PF line.  The bigger problem will be humidity.

 

I DQ'd a shooter for a PF of 162000PF instead of the 168000PF that he run 2 weeks earlier.  All loaded at the same time.  The coditions were 2 weeks earlier the humidity was about 40%, and the rainstorm that went through the day before he shot raised the humidity to 95%.

You DQ'd a shooter for power factor? What rule book were you quoting?

[RePete]

IDPA 2010 or 2011.

[MikeyScuba]

Our loads shot up to 132 from 126 in the heat of the Nevada desert. It was 105f and a few thousand feet higher than home, no zero humidity. No match’s coming up that way anytime soon but I wouldn’t risk special loads for desert conditions, but it’s tempting, lol.

[mchapman]

Other than a powder being temperature sensitive, the main thing that will effect the power factor is barometric pressure, altitude has very little to do with it in my experiance. I go from 8600 ft down to 1500 and if the barometer is the same the PF is the same.

[drewbeck]

4 hours ago, mchapman said:

Other than a powder being temperature sensitive, the main thing that will effect the power factor is barometric pressure, altitude has very little to do with it in my experiance. I go from 8600 ft down to 1500 and if the barometer is the same the PF is the same.

 

I’d argue external ballistics do not impact the PF at the chrono.. the only thing that is significant at chrono range is changes in internal ballistics

ie,  powder temp sensitivity, oal, crimp, primer, case consistency, barrel length, cleanliness, etc. 

 

barometric pressure will totally change external  ballistics, velocity, and flight path, but not at chrono ranges.

 

the reloading components you use and your processes are the only thing that will measurably impact your pf using the same gun..   

 

Basically it’s only powder temp issue to confirm one way or another