I'm just wondering how much altitude will affect velocity. If I have a load shooting a 162 grain Hornady SST in 7mm at 2,815 fps at 7,000 feet elevation, what will the velocity at 900 feet? I haven't had a chance to choron my loads here yet as there are no public shooting ranges, just clubs and those are way, way out of my price range for shooting. Is there some sort of formula for figuring the velocity at one altitude if it is known at another altitude? Thanks for any help ... Tom Purdom

Muzzle velocity is unchanged by altitude.....remaining velocity at a distance is however as less air resistance due to thinner air at higher altitudes will result in higher velocities at specific ranges. The resulting tradjectory difference however on the planet earth is minor and not to be worried about.....on the moon however their's a significant difference....you could possibly shoot a bullet into orbit there.

thank you vapodog. i am sitting at home in this snowstorm with way too much idle time on my hands, so naturally, I have to put it to use. hope you had a nice day today. Tom Purdom

Here are some figures for you to chew on, I ran your info through my Sierra Infinity program.

7,000' 900'
100 yards 0 0
200 -3.35" -3.49"
300 -12.06" -12.67"
400 -26.73" -28.37"

This is based on the info you gave, 162 grain BT Hornaday, 2815 fps, .284 cal.

thank you too Snellstrom. There is a little difference, but not that much. Tom Purdom

I have some loads that are 100fps faster in New Mexico than they are here in Nebraska. Could be a number of things though.

In my exterior ballistics program there are a number of environmental parameters you can change or play with and see some slight variations in performance. Altitude, Humidity and Temperature all have slight effects on our projectiles but what I've found is that it is relatively insignificant in the big picture. The effects are there nonetheless.