Velocity and Altitude question

[Marble]

I live 500' above sea level and hunt at 9000-11500 feet. I know ballistics change with altitude, but I'm wondering if velocity does too. If I recall correctly, if I'm shooting 3280 at 500' elevation, at 11000 or so, the velocity should be higher. I guess the sure way to know is shoot the gun through my chrony at somewhere close to that altitude, but I can't do that until I go back in October.

Or, do I put the parameters into the ballistics calculators and do they do the math for me?

 

[Barrelnut]

Velocity change in the barrel due to elevation is not a factor. A chrony 15 Ft away will probably be well within your ES to and not a factor.

If you use an app like Shooter, it calculates the altitude change for you based on the altitude/temp/pressure where you sighted in at.


It is a very good idea to actually do some practice shots and verify everything at the altitude you will be hunting at anyway IMHO.

 

[Mikecr]

It's an INTERNAL ballistic factor and wouldn't be accounted for in any EXTERNAL ballistic math.
I know it can affect tune. I don't know about muzzle velocity.

 

[Marble]

Velocity change in the barrel due to elevation is not a factor. A chrony 15 Ft away will probably be well within your ES to and not a factor.

If you use an app like Shooter, it calculates the altitude change for you based on the altitude/temp/pressure where you sighted in at.


It is a very good idea to actually do some practice shots and verify everything at the altitude you will be hunting at anyway IMHO.

Thanks for the info.

I always shoot my guns when I arrive and reconfirm zero.

My main reason for asking is I was going to have some turrets made with the drop built in. I'm just trying to make it the best I can before I go ahead with it.

 

[Marble]

It's an INTERNAL ballistic factor and wouldn't be accounted for in any EXTERNAL ballistic math.
I know it can affect tune. I don't know about muzzle velocity.

I don't understand. Can you explain more?

 

[Mikecr]

Well, different air density being pushed down a bore could affect the pressure curve a bit, affecting your accuracy. But there are a lot of variables to internal ballistics that could ultimately sum to actual muzzle velocity change -or not.

 

[Greyfox]

You are not likely to see a big change, if any in muzzle velocity, but it's still advisable to re-zero when changing locations of different altitudes. The difference in the altitude/air density, will produce a lower resistance on the bullet, producing higher retained velocities at longer ranges, thus requiring a lower elevation correction at those longer ranges. a ballistic program , like Shooter will provide the corrections when the air density/altitude info is inputed for the higher elevation.

 

[Marble]

I figured it wouldn't make too much of a difference. I always confirm zero when I travel. So I will get my new turret and give it a try. I'm going to get back there a few days earlier than normal this year anyways so maybe I'll climb up a mountain and find something close to 800 yards out and give it a few shots to confirm.