How altitude affects FPS

[Antonio999]

Hello Airgunners, greetings from Peru!!! .. This is my first post in AN... Maybe you can help me to have the right understanding to get the correct setting when I'm going to the highlands with my Rifle.
Normally I shot at sea level up to 1500ft , and my Rifle (a Cricket Tactical 2 Cal .22) works pretty well and accurate with a constant 940fps per shot.
When I go to the highlands for trout fishing I reach altitudes of 9000ft to 11000ft . Sometimes I bring my rifle with me, but I noticed that the accuracy of my shots up there change at all. My shots seems to have a flatter trajectory as the one they have at lower altitudes. Therefore, I try to fix my shots but without having all the factors which I should consider and the resources/tools that I have at home.
Does someone have tips that I have to consider when going to highlands?? What does really happen with the FPS and ballistic behaviour of the pellets? (btw I only use JSB 18.13gr and 25,39gr)
I will appreciate your help....thanks

 

[iAMzehTOASTY1]

Isn't the air thinner up higher?

 

[Impact701]

Strelok Pro works great

 

[Altair-uy]

The muzzle velocity shouldn’t change, but the air is thinner so it’s to be expected to have less air resistance hence have flatter trajectory. Best solution is to use a ballistic solver and a kestrel but the real difference might be much less than you expect, it really has a negligible effect on pcps at the distances we normally shoot.

 

[Ranchibi]

My RAW is tuned to shoot JSB 18gr @ 950fps @ sea leverl, when I shoot with my friend that lives @ 4400 foot elevation, my fps is 963fps using my ProChrono. So, yeah, flatter trajectory for sure!

 

[Airgun-hobbyist]

Search "density altitude" for some answers to the questions. There it relates to airplanes and auto racing, but would be the same principals, and the same measurements reqiured by the different ballistics apps. I get the current data numbers from various racing tracks, as well as from government airport flight data sources.

Intl Tracks « Air Density Online

Tune your engine with real-time density altitude from AirDensityOnline.com. Check out our powerful online jetting calculator or bookmark one of over 400 track's weather.

airdensityonline.com

 

[Airgun-hobbyist]

along with air being thinner at higher elevations, it is probably cooler? This will effect internal air pressure if you filled in the lower, warmer elevations.

 

[Airgun-hobbyist]

Look at getting the Strelok Pro app for whatever computer/phone that you use too. With good data inputs, it will give the best shot placement results when you make those changes in elevations.

Strelok Pro - Apps on Google Play

Professional ballistics calculator

play.google.com

http://www.strelokpro.online/index.htm

 

[Antonio999]

Thank you all for your replies... believe me that they help me a lot.
I bought Strelock, but I didn't use it yet as I should do. I will begin to use Strelock more frequently and see.
I'm still consider myself as apprentice in the PCP World... therefore and once again, I appreciate for your time and experiences shared.
Next time in the highlands I will see what happens. Take care and safe shooting.