Bullets don’t drop west of the Mississippi?

Jul 4, 2017
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#1
Bit of a clickbait header, but here goes.

Short version of the question first - for people shooting in higher DAs, what’s your approximate drop at 1000 shooting factory 140gr ammo out of a 6.5 creedmoor/260 rem? I say factory because I know most handloaders go a little faster on their MVs. Now the long version. I was shooting prairie dogs in Nebraska a few days ago and took some just for kicks shots with my 6.5 creedmoor at a sandy patch on a hill I ranged at 1015 yards. My load is factory federal 140gr going about 2740, and my trued BC is .557 (verified at 800 and 1000). With my zero DA of 1700, I need 9.1 to get to 1015, and Jbm and 4dof said to take off 0.4-0.5 Mils of elevation to make the shot (Nebraska DA was about 4600, temp 80-85). In actuality, I only needed 7.5 mils of elevation. A ~1.0 mil difference between predicted and actual seems really big. Fundamentals were solid and position was exactly the same as verifying BC back home, prone off a mat. Is there just no gravity out west? Am I crazy? One note, I was shooting east and there was about a 16ish mph wind from the south, I needed about 3.2 of wind. I have a physics degree and a rudimentary understanding of AJ, but I’m pretty sure it’s not nearly 1.0 at 1015. None of this stuff is life or death, I only shoot west of the Mississippi about once a year, just curious about what you all have to say.
 

Mordamer

Professional Know It All
May 11, 2010
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Hooker, OK
#2
My calculator also says to take 0.4 mils off for that type of change in density altitude. I have verified it in the real world and my drop was on at high altitude and low altitude. You have some other variable affecting your drop I believe.
 

Lowlight

HMFIC of this Shit
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Apr 12, 2001
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#3
Air Density

Bullets Like:

High Temperatures
High Altitude or Low Station Pressure
High Humidity

Less parasitic drag on the bullet

column.free_.gif
Fewer dots mean less drag on the bullet

Altitude is a factor of air density in shooting

Hot air excites the molecules and they move out of the way, cold air masses them together to stay warm.

cold-hot-air.jpg
 
Likes: jLorenzo

Lowlight

HMFIC of this Shit
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#4
And I will add, a lot of software does not manage this big a shift well, I normally have to adjust my MV by about 50fps moving from Colorado at about 5000 to 1000ft asl to re-true the data for the new location.

Not always but a lot of times yes, it can be software dependent on which ones require this
 
Jul 4, 2017
94
19
8
#5
Air Density

Bullets Like:

High Temperatures
High Altitude or Low Station Pressure
High Humidity
I’ve taken a few thermodynamics and chemistry courses, I understand the theoretical effects of temp and air density (please don’t take that as me being rude, I’m just explaining my background). I’m mostly confused at the massive decrease in drop that I saw. I need to increase my MV from 2740 to about 2875 to line up with what I saw, even after accounting for the DA shift and AJ, which just seems wild to me.
 
Jul 4, 2017
94
19
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#7
You zero at 100 right, why do you need to turn that stuff on it does not extend downrange

The air is less dense, as simple as it gets, the other stuff is just window dressing
Yep I verified my zero the prior morning at 100. I rarely/never use AJ, I was just trying to find possible explanations. I’ll just write down the dope I saw and keep it in mind for the future I suppose.
 

Skookum

Flattus Domini
May 6, 2017
691
572
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Your mom's
#8
I think this whole Density Altitude thing fucks people up.

I wish shooters would go back to just using station pressure for exterior ballistics and temperature for adjusting powder burn rate (interior ballistics). Whoever thought it was a good idea to use Density Altitude for a ballistics program needs a swift kick in the nuts.
 
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