Convert fps at 1300 ft of elevation to fps at 6500 fps


Dec 20, 2021
I want to have my Leupold Custom Dial Done and the Tech at Leupold advised me to send me the information where I will be doing most of my hunting (Montana) instead of where I did my testing (Minnesota). I'm having a brain fart trying to figure this out. If my 270WSM 150g AccuBond is going 2989FPS at 1300 feet of elevation, what will it be going at the muzzle at 6500 feet of elevation? I tried to look online for a conversion but couldn't find one. TIA. PS. If there is some sort of table please provide a link.

Temperature can impact how powder burns so it obviously effects muzzle velocity, so I agree with that statement. Altitude doesn't always equate to decrease in temperature.
Temperature and altitude are related in that they both affect air density and therefore the ballistic performance of a bullet. Lower altitudes result in denser air, therefore more drag on the bullet and more bullet drop. Higher altitudes result in thinner air, therefore less drag on the bullet and less bullet drop.
The atmospheric pressure goes down as the elevation goes up. The lower pressure reduces the drag on the bullet and therefore the bullet retains more energy and velocity at longer ranges. The starting velocity doesn't change no matter the elevation, with all else being equal.
Temperature and altitude are counter to each other. A bullet drops less in higher altitude while lowering temperature makes the bullet drop more. You can drive yourself more crazy trying to figure out what you want on a custom dial.
I talked with the Tech at Leupold today. He told me just to use the velocity from MN for my custom dial. Basically, for most hunting ranges he said it won't matter so I ordered my custom dial today. Thanks for the replies.
Easy misconception.

At altitude your rifle will likely shoot flatter, because there is less drag, so the bullet retains velocity better. Muzzle velocity remains the same, but velocity at 300+ yards may well be noticeably faster & trajectory flatter.

I think we've all been saying this, in different ways. :)

Best of luck on your upcoming hunts! Guy
It does not. It affects Ballistic coefficient which is based on altitude. The higher you are the less denser the air is.
BC does change some but air density is more critical and has a larger effect. A bullets profile doesn't drastically change but how the air effects it does change with altitude/humidity/temperature.