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ok, dumb question but I'll ask anyway - how much does altitude (temp & pressure) effect bullet ballistic performance & drop ?
Most of my load dev done at ~ 300 ft above SL @ 17C +/- 5, most hunting at or near bush line say 2800 ft alt 5C +/- 5.
Assuming good weather ( atmospheric pressure at 1010 - 1020 hPa at SL) after correcting atm pressure for altitude and assumed temps above it looks like there's bugga all difference ? Yeah or nah ?
heaps and none, depends how far you plan to shoot.
For normal load dev at say 1-200 y/m you wont see shit
I can get a .5moa variance at 500 yards just by messing with temp and pressure, get out past 700 and it makes a big difference
Yep, should have included above - assume out to 500 - 800 yards. Decent high BC pills, 7mm or 30cal.
Work on minus one inch hg or33hpa per 1000ft.
Enough of a difference to make a shot a poor hit rather than a good one.
Higher you go the 'thinner' the air gets, bullets don't require as much 'up'.
Put up your projectile and velocity and zero range and I will compare on shooter.
Spend $400 on a 2700 kestrel and no more guessing your elevation.
Next question
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7mm 150 ELdx 2900 FPS , 168 Berger CH 2930 FPS, 162 AMAX 2980 FPS.
30 cal 180 EH Berger 3040 FPS
Useing the 150eldx and 1000hpa at sealevel and 834.5hpa for 1500m asl assuming the same temp and humidity and a level shot at 800y I getQuote:
Originally Posted by chainsaw
Drop= 158.6" vs 146.9" @800y
Windage in 5mph from 90 deg= 21" vs 16.8"
So if drop worked out at sea level and hunting/shooting in the tussock you could be shooting 11 or more inches high.
The forum wont let me upload the screenshots because they are too big a file apparently.
Thanks Cam, using Hornady calculator I was coming up with 7-8inch difference at 2800 ft alt and assuming air temp of 5 C
Essentially, reduced air pressure has the same effect as increasing ballistic coefficient by the same amount.
This thread goes into how much pressure typically changes with altitude.
Thats probably pretty close.....I went 1500m as bushline round here is more 1300-1400m so a bit higher than 2800ft
If you run the numbers environmentals don't really matter out to around 500m (can be an inch or so difference)
Once you start getting into longer ranges they do start haveing an effect
You need to be quite precise with them once you start shooting past 1000m. i find that inside 1000m an educated guess on temperature and elevation (these matter most) is plenty good enough to hit a 1-2 MOA target
You don't need to stress buy a kestrel just yet, particularly if you're planning on keeping shots inside 1KM