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Its On: The Second Amendment Preservation Precision Rifle Challenge

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OnTheFly:

--- Quote from: kozball on May 14, 2013, 10:19:54 PM ---Been trying to get a grasp on this Density Altitude thing.

A friend at work just got his pilot license. He flies small Cesna type airplanes out of North Omaha. As a pilot, he has firsthand knowledge of DA. He told me that as of this AM at 11:00, the DA at Blair airport was just short of 4000'. This is from a set altitude of close to 1300'.

Now I took this info and went to Federal Ballistics website and entered for 175 SMK 308cal. 1st entry at 1300' and temp of 70. 2nd entry at 3500 ' and temp of 70. Both with 200yd zero.

The trajectory diff was only 1.3" at 500yds, 2.8" at 600yds, 4.9" at 700yds, up to 19.3" at 1000 yds.

I found this incredible, as I had no idea that around here (Omaha area) that we could have such a huge swing in altitude which affects ballistics by a huge amount when trying to engage a 24" target.

Just an FYI and hope I am correct. :-\

--- End quote ---

Did this calculator ask for any kind of barometric pressure or pressure altitude?  Calculating density altitude starts by taking your elevation and correcting it for non-standard pressure which results in the "Pressure Altitude".  Then you take the Pressure Altitude and adjust it for non-standard temperature which gives you the "Density Altitude".

High temperatures, low pressure, and humid air will all increase the Density Altitude.

Fly

kozball:

--- Quote from: OnTheFly on May 15, 2013, 01:38:36 AM ---Did this calculator ask for any kind of barometric pressure or pressure altitude? 
--- End quote ---

Not sure how the info is calculated. He has an app on his phone and dials up the conditions at each airport that he may fly to. I assume that the data is calculated at each airport. I'll see if I can find out what the app is.

bkoenig:
I've been playing with different altitudes and barometric pressures and it's amazing how much difference it makes at long ranges. According to the charts, with my 20" barreled .308 I'm able to keep an 180 gr SMK supersonic well past 1000 yards if I'm at Lincoln elevation, but drop it down near sea level and it goes subsonic around 950 or so.  At lower elevations it looks like I'll run out of clicks on my scope, but around here I have plenty to spare.

I wanted to try some 178 gr Amax or 175 SMK's, but they're like hen's teeth right now.  From what I've read the 180 SMK isn't the best long range bullet because of the shape of its tail.  Hopefully I can use what I have to work up a useable load, and when some Amax bullets become available I can give them a try.

kozball:
My guy at work uses the program called Foreflight and then some link called metars ?
 
Like he can punch up KK46 for Blair, then go to the metars and the info is there.

bkoenig:
I just ordered some AR500 targets.  One 12" gong and one half size IPSC silhouette, paid a hair over $80 shipped which seems to be pretty cheap.  Now if I can just get some time to try and stretch the legs on my rifle....

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