Author Topic: External Ballistics  (Read 2416 times)

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External Ballistics
« on: January 28, 2013, 10:40:20 PM »

Offline ID#5

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The Speed of Sound in Air


*The reason the speed of sound in air is important is a rifle bullet is only considered accurate while in supersonic flight, assuming it starts out with a supersonic muzzle velocity OR the reason the speed of sound in air is important is a rifle bullet is only quiet (silenced) while in subsonic flight, assuming it starts out with a subsonic muzzle velocity.


*Maximum effective range for any ammunition is limited to its flight until it begins its transonic flight. Twist rate or Spin is NOT a factor.
(some bullets are not affected much by transonic flight, some are, you just have to check yours)


*The speed of sound in air is dependent on air temperature ONLY.
As air temperature decreases, the speed of sound in air decreases.  As air temperature increases, the speed of sound increases.


*Barometric or air pressure is NOT a factor. The reason is air pressure and the density of air are proportional to each other at the same temperature.


*Humidity has a small impact on the speed of sound in air.  The speed of sound is slightly faster in more humid air.

For example:
At 32F, the speed of sound in air is 2 FPS faster at 100% humidity than at 0% humidity.
At 100F, the speed of sound in air is 11 FPS faster at 100% humidity than at 0% humidity.


*As the bullet transitions from supersonic to transonic to subsonic it gets buffeted by the shockwave in front of it and the bullet can start to yaw and pitch and the heavier tail starts to move around and CAN cause the bullet to lose its consistency/predictability/accuracy. 


*As the bullet is Transonic it is in a period of destabilization.  This period of destabilization can/will cause the bullet to tumble at the very least or it will be deflected off its original flight path, and is therefore unpredictable on its point of impact. THIS DEPENDS ON THE BULLET


*A supersonic bullet gives off a sonic boom similar to an aircraft, but is heard as a crack rather than a boom.


*Supersonic burnout 40M before target in margins for a hit-generally.


*Transonic is defined as about for aircraft=  .8 Mach to Mach 1.2  This is because different parts of the aircraft (because of angles, etc) will be supersonic while others will be sub or transsonic.


*This transonic area can also be used for bullets.
Formula for Mach in air = velocity of object divided by speed of sound.
Velocity of object (in this case, bullet)/ Speed of sound


*The Speed of Sound in Air Table
The Speed of Sound in air at 0% relative humidity.


*Air Temperature in Fahrenheit    Speed of Sound in air  in Feet Per Second
-40F    1004 FPS
-20F    1028 FPS
0F       1051 FPS
10F     1062 FPS
20F     1074 FPS
30F     1085 FPS
40F     1096 FPS
50F     1106 FPS
60F     1117 FPS
70F     1128 FPS
80F     1138 FPS
90F     1149 FPS
100F    1159 FPS
110F    1169 FPS
120F    1180 FPS
130F    1190 FPS
140F    1200 FPS
« Last Edit: January 28, 2013, 10:57:28 PM by ID#5 »
How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D

Re: External Ballistics
« Reply #1 on: January 28, 2013, 10:43:18 PM »

Offline ID#5

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Barometric Pressure


*Standard Barometric Pressure is 29.53Hg for ammunition or 29.92Hg. for aviation at sea level.


*Hg. = inches of Mercury


*THE BELOW IS ALL BASED ON UNCORRECTED PRESSURE


*Barometric Pressure ABOVE 29.53Hg. (example 30.41Hg.) means that there is higher air pressure and the bullet will encounter more air resistance(drag), therefore, you will need more elevation on the rifle’s sights or Line of Bore to compensate.


*Barometric Pressure BELOW 29.53Hg. (example 27.10Hg.) means that there is lower air pressure and the bullet will encounter less air resistance (drag), therefore, you will need less elevation on the rifle’s sights or Line of Bore to compensate.


*Barometric Pressure higher than 29.53Hg. means a shorter supersonic range (a decrease in Maximum Effective Range).


*Barometric Pressure lower than 29.53Hg. means a longer supersonic range (an increase in Maximum Effective Range).


*Barometric Pressure corrections are based upon True Range NOT Slant Range.


*Air Pressure is 14.7 Per Square Inch at Sea Level.


*Use Absolute Air Pressure (Station Pressure or uncorrected).  Air pressure factored for altitude/elevation is called altitude Corrected Pressure.


*As altitude/elevation above sea level increases, barometric pressure decreases
Barometer readings decrease approx. 1Hg. per 1,000 feet increase in altitude/elevation from sea level.
(for example, assume you were at 3,000 feet above sea level
subtract 3Hg. from 30Hg. and your approximate Pressure would be 27Hg.)

*Google Earth can be used to determine what the elevation is for your shooting location.


*Barometric pressure and altitude are the same effect as far as external ballistics goes.  If you can determine the pressure and can correct for it, you are correcting for altitude


*Highest recorded air pressure reading is approx. 32.0Hg.  Once in Siberia, Russia in 1968 and once in Mongolia in 2001.

*Lowest recorded air pressures at Sea Level are typhoons and hurricanes at approx. 26Hg.  Lowest recorded on summit of Mt. Everest was 7Hg.



« Last Edit: January 28, 2013, 11:01:45 PM by ID#5 »
How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D

Re: External Ballistics
« Reply #2 on: January 28, 2013, 10:45:02 PM »

Offline ID#5

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Air Temperature

*Standard Air Temperature is 59F for ammunition for ballistic calcs.


*Air Temperature ABOVE 59.00F means that the air is thinner and the bullet will encounter less air resistance (drag), therefore, you will need less elevation on the rifle’s sights or Line of Bore to compensate.


*Air Temperature BELOW 59.00F means that the air is thicker and the bullet will encounter more air resistance (drag), therefore, you will need more elevation on the rifle’s sights or Line of Bore to compensate.


*Air Temperature higher than 59F means a longer supersonic range (an increase in Maximum Effective Range).


*Air Temperature lower than 59F means a shorter supersonic range (a decrease in Maximum Effective Range).



How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D

Re: External Ballistics
« Reply #3 on: January 28, 2013, 10:46:39 PM »

Offline ID#5

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Humidity


*Standard Humidity is 78% for ammunition for ballistic calcs.


*Humidity’s effect on a bullets trajectory is minimal. 


*The change in impact from 0% humidity to 100% humidity at 1,000 yards is 3 inches at 59F, 29.92Hg (aviation, sea level, .308Win)
At 100F the change in impact from 0% humidity to 100% is 7 inches. Again at 29.92Hg at 1000 yards.
At 80F the change in impact from 0% humidity to 100% humidity is 1.2 MOa at 2,000 yards(27.8HG, .625BC)


*More humid air has less air resistance


*Dry air is more dense than humid air


*The molecular weight of water is lower than the molecular weight of air (18 vs. 29) for any specified atmospheric temperature and pressure the density of humid air is lower than the density of dry air.  Consequently there is more drag on a bullet in dry air than in humid air, provided the temperature and barometric pressure remained the same-from the 50th anniversary Sierra reloading manual.


« Last Edit: January 28, 2013, 11:03:03 PM by ID#5 »
How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D

Re: External Ballistics
« Reply #4 on: June 27, 2013, 06:24:23 PM »

Offline J Mack

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An Introduction to Air Density and Density Altitude Calculations,


         
What is density altitude?
http://wahiduddin.net/calc/density_altitude.htm





 
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Re: External Ballistics
« Reply #5 on: December 03, 2013, 03:42:58 PM »

Offline The Admin

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Steve, what is the source for this information... thanks
I got a fever, and the only prescription is more 1911's .

Re: External Ballistics
« Reply #6 on: December 03, 2013, 05:57:09 PM »

Offline ID#5

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Steve, what is the source for this information... thanks

what part?
I pulled info from many diffrent places for the posts on Speed of Sound, Pressure, Temp, Humidity

How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D

Re: External Ballistics
« Reply #7 on: December 03, 2013, 06:47:03 PM »

Offline Luvmy45

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Mostly the speed of sound in air as it relates to transonic issues with the bullet...

Re: External Ballistics
« Reply #8 on: December 03, 2013, 07:25:16 PM »

Offline ID#5

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The Speed of Sound stuff about bullets is mostly from the Dean Michaelis book "the Complete .50 caliber Sniper" or a title similar to that.
[paragraphs 1, 2, 7, 8, 10]

The other info in the Speed of Sound post is from using google and finding data on diffrent universities and science web pages about SoS.
« Last Edit: December 03, 2013, 07:26:54 PM by ID#5 »
How much is that in Mils? - JMack
March 2, 2013


It's completely legal.   The only problem is that it puts you into FR Class (Full Retard), and you might be the only one in the entire country running FR.   Of course, it would set you up for 1st Place in your class, everytime you shoot. 
Big D