Velocity and pressure change with altitude?

[thx997303]

So, I was in TX near sea level when I worked up all of my loads, and now I'm back in Utah at around 6000+ feet.

What kind of change can I expect to see?

I will of course go shoot and see, just interested in the discussion.

[303Guy]

Interesting question. When you do your tests, try to have the rounds at the same temperature as they were at sea level.

[thx997303]

Temperature won't be an issue. But humidity has changed too. Much drier here.

Aside from which, all I will be able to use to judge will be accuracy and POI.

No chrony unfortunately.

[fredj338]

Velocity should go up slightly, thinner air, but pressures should remain unchanged unless temps go up or down.

[sagacious]

Altitude makes no difference in terms of pressure generated by the cartridge.

You can shoot your handloads at sea-level, or Death Valley, or the summit of Mt Everest, or outer space. No worries about altitude affecting safe pressure levels. The difference in atmospheric pressure between Death Valley and outer space is only about 15psi. One gets more pressure variation than that from shot-to-shot.

[runfiverun]

you could see a slight change in the boolits path of travell in the higher altitude though.
less wind resistance.
around slc the altitude is 4300 feet, texas airc is @500.
i never noticed any change from 4300 to 6,300.

[John Boy]

Temperature won't be an issue
The only real time temperature is a factor is if a shooter has reloads of black powder. Then there is a fouling change with a relative humidity (RH) above or below 40%. RH is normally temperature impacted

[lwknight]

You will get better long range velocity in thinner air. It won't be enough to help the trajectory in any noticeable way though. Your case is sealed so humidity won't matter.

[mike in co]

The only real time temperature is a factor is if a shooter has reloads of black powder. Then there is a fouling change with a relative humidity (RH) above or below 40%. RH is normally temperature impacted

lol
lol
lol
ya got to be kidding me......


ask any high power shooter, any br shooter......


if he had some load data we could run the numbers in quickload and publish the differences for you.

[303Guy]

Relative humidity would be of interest to black powder shooters as it effects condensation on the salty deposits in the bore. Absolute humidity would be of interest to long-range shooters as it effects drag on the bullet.