How much does elevation affect velocity???

[chad44]

I origiNally chronographed my velocity at 8000 feet in elevation and about 60 degrees at 2900 fps. Reccently I was at 4300 feet and 85 degrees and it was clocking at 3020 fps. Is this normal?

 

[barnesuser28]

it was most likely the difference in temperature. what powder were/are you using

 

[Jordan Smith]

Elevation doesn't affect your muzzle velocity, so much as it does the drag of the air on the bullet in flight.

The temperature change is likely what caused the MV increase.

 

[chad44]

I was using H1000. That's why I figured temp shouldn't play a part since its the extreme powder. I was using a buddies chrony the first time and bought my own for the last reading. They are the same chrony though.

 

[WildRose]

I was using H1000. That's why I figured temp shouldn't play a part since its the extreme powder. I was using a buddies chrony the first time and bought my own for the last reading. They are the same chrony though.

Thinner air at higher elevations (relative to low) gives less resistance.

Temperature and the differences between the two chrony's (even if they are the same brand/model, would be responsible for the apparent increase.

Barometric pressure can have such an effect as well.

 

[Jordan Smith]

^ Yup. If you used two different chrony's to gather your speed data, then all bets are off. The only way to get meaningful data is to keep everything consistent, and only change one variable at a time. That's very difficult in the real world, when shooting, due to different RH, atmos. pressure, temp, load variability, etc. If you can keep everything the same, and just change elevation, you'd be able to see the true difference.

Try using the same chrony in both situations, and you'll have a much better idea.

 

[chad44]

Ok. I will try Barrowing his again and compare side by side. Thanks

 

[royinidaho]

(85* - 60*)=25* temp increase.

Mv increase should have been on the order of 12 FPS MV

However, unless your ES and SD are in single digits you'll never notice it.

If your and you're buddies chronys are Chronys brightness changes will change measured fps more than 12 FPS when a cloud passes over. (my experience)

 

[Bravo 4]

Instead of testing them side by side shoot through both at the same time (lined up) and compair.

 

[chad44]

Great idea. Stupid to say this but I never thought of that. Saves ammo and gives you the true difference of the two. Thanks