Load adjustment for altitude

[sdean]

Going from sea level to 1800 above at 1000 yds. How much speed will my load pick up!? 260AI. 140 hybrids at 2950. Could use a lil insight or help..

 

[XTR]

It won’t pick up speed, but it will get there with less elevation. The air is thinner So it affords less resistance to the bullet. Go to JBM and put in the two different altitudes with your chosen bullet and you can see the difference in your come up to 1000 yards

https://www.jbmballistics.com/cgi-bin/jbmtraj-5.1.cgi

when Jade won the FCNC at Raton (6700+ASL) he shot the same load he shoots at Shreveport.

 

[Medic505]

JBM Ballistic Calculations - Trajectory

Ha, Wade beat me to it.. So simple even F-TR chooters can figure it out....

 

[sdean]

JBM Ballistic Calculations - Trajectory

Ha, Wade beat me to it.. So simple even F-TR chooters can figure it out....

I had already checked there and it showed a loss off 70fps at 1000yds. That's what got me wondering. Thanks

 

[PatMiles]

So simple even F-TR chooters can figure it out....

 

[Paw precision]

The higher elevation will yield an increase in bullet speed at elevation. There is less resistance on the bullet.

 

[watercam]

For me changing from 150' elevation near the coast to 4600' at the high desert at 1000 yds. showed a 2 moa higher hit. JBM confirmed as well. May not be too bad for you.

 

[chromatica]

Here you go:

At Sea Level:
G7: .312
Mv: 2950
Scope Height 1.95 in (my scope height)
Baro: 29.92 in Hg
Temp: 59 F
At 1000 yards
Drop: -264.1 in
Velocity: 1612 fps
Mach 1.44
Time of flight: 1.372 sec

At 1800 ft elevation
Baro: 28.10 inHg
Temp 59
At 1000 yards:
Drop: -255.3
Velocity: 1682 fps
Mach: 1.51
Time of flight: 1.350 sec

That's a difference of 9 inches in vertical drop.
You will pick up 70 fps in velocity at the target.