Drop in rain?
- Thread starter AKD
- Start date
- Location
- Somewhere on the Hudson Bay Coast
Humid air is less dense than dry air, so if the change was due to humidity your group should have risen not dropped. If the rain became heavy, perhaps the image of the target became displaced as can happen with mirage. As for a changed in POI due to the bullet passing through drops of water, I too have read it makes no difference, but perhaps the reference was over normal shooting ranges, and at long range there might be a difference. I seem to recall that a bullet would have a different POI if it was wet prior to being fired, so if true, and your ammo or bore got wet, that might account for the drop.
Nope ammo was dry in a handloaders ammo box. Only open to load in the gun.
Had no problem seeing the target. Had a nice group and 5 rounds on target, sun came out and next thing I know I'm over shooting. This is all with in 5min.
Had no problem seeing the target. Had a nice group and 5 rounds on target, sun came out and next thing I know I'm over shooting. This is all with in 5min.
It's not so much the humidity that would cause the drop. Rain has no real effect. What might be the issue is when it rains or is about to rain you get a temperature drop and at long ranges that definitely influences bullet flight at long range. Its good dope for next time. Log all the details. Your just creating good dope for your rifle and shooting conditions.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
AKD were you getting your POI shifts during your string, as it rained and then stopped raining?
If so that is pretty odd (and interesting). I've never been able to notice a POI effect due to rain (or for that matter to changes in lighting conditions, or mirage).
If so that is pretty odd (and interesting). I've never been able to notice a POI effect due to rain (or for that matter to changes in lighting conditions, or mirage).
Ya light and mirage never effected me either. Cheek weld yes but..
I was zeroed on giving good shots well it was raining than the sun came out, rain stopped, and next thing I know I'm missing. I fire at the dirt and ya hitting high. Dialed down 7 clicks and back on target for the last 7 shots.
Thats why I posted this. Thought it was intresting. Not like I pick very rainy days to go shooting much. I've shot long distance in the rain befor but usually it's a constant rain.
Windage correction had no effect.
I was zeroed on giving good shots well it was raining than the sun came out, rain stopped, and next thing I know I'm missing. I fire at the dirt and ya hitting high. Dialed down 7 clicks and back on target for the last 7 shots.
Thats why I posted this. Thought it was intresting. Not like I pick very rainy days to go shooting much. I've shot long distance in the rain befor but usually it's a constant rain.
Windage correction had no effect.
It is possible when the sun came out it caused a increase in water vapor this would increase humidity making the air less dense. As explained below water vapor is less dense then diatomic oxygen and diatomic nitrogen the major components of air.
Shooting in rain can have many variables that may be overlooked. Please read below I spent allot of time typing this out
Density of Dry Air
The density of dry air can be expressed as:
ρa = 0.0035 pa / T (1)
where
ρa = density dry air (kg/m3)
pa = partial pressure of air (Pa, N/m2)
T = absolute dry bulb temperature (K)
Density of Water Vapor
The density of water vapor can be expressed as:
ρw = 0.0022 pw / T (2)
where
pw = partial pressure water vapor (Pa, N/m2)
ρw = density water vapor (kg/m3)
T = absolute dry bulb temperature (K)
Density of Moist Air - an Air Vapor Mixture
The amount of water vapor in air influences density. Water vapor is a relatively light gas compared to diatomic Oxygen and diatomic Nitrogen - the dominant components in air.
When water vapor content increases in the moist air the amount of Oxygen and Nitrogen decreases per unit volume and the density decreases because the mass is decreasing.
* Dry air is more dense that humid air!
Based on the specific volume of moist air density can be expressed as:
ρ = 1 / v
= (p / Ra T) (1 + x) / (1 + x Rw / Ra) (3)
where
v = specific volume of moist air per mass unit of dry air and water vapor (m3/kg)
Ra = 286.9 - the individual gas constant air (J/kg K)
Rw = 461.5 - the individual gas constant water vapor (J/kg K)
x = specific humidity or humidity ratio (kg/kg)
p = pressure in the humid air (Pa)
Density of dry air can be expressed as:
ρda = p / Ra T (4)
where
ρda = density dry air (kg/m3)
Combining (4) and (3):
ρ = ρda (1 + x) / (1 + x Rw / Ra) (5)
The gas constant ratio between water vapor and air is
Rw / Ra = (461.5 J/kg K) / (286.9 J/kg K)
= 1.609
Inserting the ratio in (5):
ρ = ρda (1 + x) / (1 + 1.609 x ) (6)
Note! As we can see from (6) increased moisture content will reduce the density of the moist air - Dry air is more dense than moist air.
Sponsored Links
Related Topics
* Air Psychrometrics - The study of moist and humid air - air condition - psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content and more .
* Gas and Compressed Air - Gas properties, capacities of pipelines, sizing of relief valves - air, LNG, LPG and more
Sponsored Links
Related Documents
* Air Composition - Dry air is a mechanical mixture of nitrogen, oxygen, carbon dioxide and more
* Densities and Specific Volumes of Dry Air and Water Vapor - Densities and specific volumes of dry air and water vapor at temperatures ranging 225 to 900 degF (107 to 482 degC)
* Density of Moist Air - Density of moist air - pressure ranging 75 - 1000 mm Hg
* Humid Air and the Ideal Gas Law - The Ideal Gas Law relating pressure, temperature, and volume of an ideal or perfect gas used for air with water vapor - or moist air
* Humidity Ratio of Air - Humidity ratio (GPP) is the ratio between actual mass of water vapor present in moist air - to the mass of dry air
* Molecular Mass of Air - Dry air is a mixture of gases where the molecular weight can be calculated by adding the weight of each component
* Specific Volume of Moist Air - Specific volume is defined as the total volume of humid air per mass unit of dry air
* Water Vapor - Weight in Air - Weight of water vapor in air
* Water Vapor and Saturation Pressure in Humid Air - The saturation pressure of water vapor in moist air varies with temperature
Shooting in rain can have many variables that may be overlooked. Please read below I spent allot of time typing this out
Density of Dry Air
The density of dry air can be expressed as:
ρa = 0.0035 pa / T (1)
where
ρa = density dry air (kg/m3)
pa = partial pressure of air (Pa, N/m2)
T = absolute dry bulb temperature (K)
Density of Water Vapor
The density of water vapor can be expressed as:
ρw = 0.0022 pw / T (2)
where
pw = partial pressure water vapor (Pa, N/m2)
ρw = density water vapor (kg/m3)
T = absolute dry bulb temperature (K)
Density of Moist Air - an Air Vapor Mixture
The amount of water vapor in air influences density. Water vapor is a relatively light gas compared to diatomic Oxygen and diatomic Nitrogen - the dominant components in air.
When water vapor content increases in the moist air the amount of Oxygen and Nitrogen decreases per unit volume and the density decreases because the mass is decreasing.
* Dry air is more dense that humid air!
Based on the specific volume of moist air density can be expressed as:
ρ = 1 / v
= (p / Ra T) (1 + x) / (1 + x Rw / Ra) (3)
where
v = specific volume of moist air per mass unit of dry air and water vapor (m3/kg)
Ra = 286.9 - the individual gas constant air (J/kg K)
Rw = 461.5 - the individual gas constant water vapor (J/kg K)
x = specific humidity or humidity ratio (kg/kg)
p = pressure in the humid air (Pa)
Density of dry air can be expressed as:
ρda = p / Ra T (4)
where
ρda = density dry air (kg/m3)
Combining (4) and (3):
ρ = ρda (1 + x) / (1 + x Rw / Ra) (5)
The gas constant ratio between water vapor and air is
Rw / Ra = (461.5 J/kg K) / (286.9 J/kg K)
= 1.609
Inserting the ratio in (5):
ρ = ρda (1 + x) / (1 + 1.609 x ) (6)
Note! As we can see from (6) increased moisture content will reduce the density of the moist air - Dry air is more dense than moist air.
Sponsored Links
Related Topics
* Air Psychrometrics - The study of moist and humid air - air condition - psychrometric charts, Mollier diagrams, air temperature, absolute and relative humidity, moisture content and more .
* Gas and Compressed Air - Gas properties, capacities of pipelines, sizing of relief valves - air, LNG, LPG and more
Sponsored Links
Related Documents
* Air Composition - Dry air is a mechanical mixture of nitrogen, oxygen, carbon dioxide and more
* Densities and Specific Volumes of Dry Air and Water Vapor - Densities and specific volumes of dry air and water vapor at temperatures ranging 225 to 900 degF (107 to 482 degC)
* Density of Moist Air - Density of moist air - pressure ranging 75 - 1000 mm Hg
* Humid Air and the Ideal Gas Law - The Ideal Gas Law relating pressure, temperature, and volume of an ideal or perfect gas used for air with water vapor - or moist air
* Humidity Ratio of Air - Humidity ratio (GPP) is the ratio between actual mass of water vapor present in moist air - to the mass of dry air
* Molecular Mass of Air - Dry air is a mixture of gases where the molecular weight can be calculated by adding the weight of each component
* Specific Volume of Moist Air - Specific volume is defined as the total volume of humid air per mass unit of dry air
* Water Vapor - Weight in Air - Weight of water vapor in air
* Water Vapor and Saturation Pressure in Humid Air - The saturation pressure of water vapor in moist air varies with temperature
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To be more scientific you could check temp, pressure and humidity before and during the rain. You might find a difference consistent with your POI shift.
A 3" drop change at 800 yards might be something like 4 degree temp change or 0.2mmHg pressure change.
If the effect was caused by raindrops hitting the bullet, it would depend on how many raindrops hit the bullet, and you would get stringing rather than a uniform change in point of impact. I would expect.
A 3" drop change at 800 yards might be something like 4 degree temp change or 0.2mmHg pressure change.
If the effect was caused by raindrops hitting the bullet, it would depend on how many raindrops hit the bullet, and you would get stringing rather than a uniform change in point of impact. I would expect.
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
rnbra-shooter
CGN Ultra frequent flyer
- Location
- New Brunswick
Wow; a 2-3" shift in POI at 100 is almost unbelievably huge.
Might be a little more around 2. The point is when I Zeroed I was bang on, zero re confirmed with two more 5 rd groups.
the rain was pretty heavy. The next time I shot the rain had passed and my first shoot was a 20rd group from the prone in 2min. Group was good but the poi was clearly high from my point of aim.
Asked a few of the others and they noticed the same.
*note*. With shooting in rain I've never had rain actually open up my groups. But noticing this now, if I'm out hunting in the rain I'll most likely adjust by at least 1moa. At least until I try this a few more times and prove my self wrong.
the rain was pretty heavy. The next time I shot the rain had passed and my first shoot was a 20rd group from the prone in 2min. Group was good but the poi was clearly high from my point of aim.
Asked a few of the others and they noticed the same.
*note*. With shooting in rain I've never had rain actually open up my groups. But noticing this now, if I'm out hunting in the rain I'll most likely adjust by at least 1moa. At least until I try this a few more times and prove my self wrong.
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