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Discussion in 'Long Range Hunting & Shooting' started by zookman, Mar 25, 2011.
If I zero my rifle with 80degree temp. the shoot it when its 40 out will I b low or high ?
J E CUSTOM
I would have thought high ! Thinner air ! Me n my daughter drag raced for yrs . The corrected altitude would be lower in cooler temps!
Low....not much but lower.
Your powder will not burn as hot resulting in lower muzzle velocity.
If you zero at 80 degrees and temp drops to 40, same altitude, bullet will be lower. As far as shooting at 40 degrees at higher altitude, I'd be interested to know if thinner air compensates for cooler temp.
This also depends on other factors. Barometric pressure, humidity and also the distance you are shooting at. I use Density Altitude(which puts all those numbers together) when figuring out my drop charts and look at my Kestrel 4000 before shooting to determine my bullet drop.
Your zero should be almost identical if you are shooting less than 300yds. My zero is 100yds for all my rifles, others have 50 and some others do 200 or 300yds. I've been to Colorado at 8000ft to shoot and to Corpus Christi, TX where its 20ft above see level and my zero was almost the same, but distance was way off with the two different altitudes/pressure/humidity/etc...
For a high BC bullet( 7mm , 6.5-284) at 1000yards 40 degrees cooler will result in the POI being about 7 inches LOW. At 750 yards the difference would be 2 inches LOW and there would be very little difference from 500 yards down. 40 degrees temperature change is almost identical to a 2000 foot change in elevation so yes they can cancel each other out. They must be in opposite directions to cancel out .
It does all else being equal. I use 500' elev. = 10 degrees temp at about 1000 yds......Rich