We were at the range today shooting .22’s off the bench at 100 yards. I had the rifles zeroed pretty well. We were trying to shoot pennies off the top of a 2x4. We were managing to hit one every 4 or 5 shots. A very light rain storm rolls in and both .22’s rifles started hitting about 2” low. Would a change in air pressure change the impact point that much at 100 yards with a .22? When the storm passed the problem seemed to correct it’s self. I realize that we could have just got into sum slower ammo. Has anyone experienced this?
Weather affecting 100 zero?
- Thread starter jeffm
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Re: Weather affecting 100 zero?
I don't know anything about atmospheric pressure affecting the zero of a rifle. I'm sure that it does, but don't know enough about it to give an answer.
I would assume though that the light rain would definately affect the zero. The moisture in the air is going to cause a resistance or obstacle for the bullet to travel through. As the bullet travels through the rain and humidity, these are going to slow the bullets velocity because the bullet now requires more energy to pass through. A slower bullet is going is going to take longer to reach the target. With the increased flight time, the POI is going to drop below the original zero. When the rain lifted, it makes sense that the original POI would be returned as the resistance was removed from the trajectory.
I don't know anything about atmospheric pressure affecting the zero of a rifle. I'm sure that it does, but don't know enough about it to give an answer.
I would assume though that the light rain would definately affect the zero. The moisture in the air is going to cause a resistance or obstacle for the bullet to travel through. As the bullet travels through the rain and humidity, these are going to slow the bullets velocity because the bullet now requires more energy to pass through. A slower bullet is going is going to take longer to reach the target. With the increased flight time, the POI is going to drop below the original zero. When the rain lifted, it makes sense that the original POI would be returned as the resistance was removed from the trajectory.
Re: Weather affecting 100 zero?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Situation Normal</div><div class="ubbcode-body">I don't know anything about atmospheric pressure affecting the zero of a rifle. I'm sure that it does, but don't know enough about it to give an answer.
I would assume though that the light rain would definately affect the zero. The moisture in the air is going to cause a resistance or obstacle for the bullet to travel through. As the bullet travels through the rain and humidity, these are going to slow the bullets velocity because the bullet now requires more energy to pass through. A slower bullet is going is going to take longer to reach the target. With the increased flight time, the POI is going to drop below the original zero. When the rain lifted, it makes sense that the original POI would be returned as the resistance was removed from the trajectory. </div></div>
Check out a psychrometric chart and you will find out that higher humidity equals lower air density...not higher as stated.
just sayin'
FWIW
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Situation Normal</div><div class="ubbcode-body">I don't know anything about atmospheric pressure affecting the zero of a rifle. I'm sure that it does, but don't know enough about it to give an answer.
I would assume though that the light rain would definately affect the zero. The moisture in the air is going to cause a resistance or obstacle for the bullet to travel through. As the bullet travels through the rain and humidity, these are going to slow the bullets velocity because the bullet now requires more energy to pass through. A slower bullet is going is going to take longer to reach the target. With the increased flight time, the POI is going to drop below the original zero. When the rain lifted, it makes sense that the original POI would be returned as the resistance was removed from the trajectory. </div></div>
Check out a psychrometric chart and you will find out that higher humidity equals lower air density...not higher as stated.
just sayin'
FWIW
Re: Weather affecting 100 zero?
2" is quite a bit, but still possible. If it was entirely due to the weather, I couldn't say. But, the weather does have quite a bit impact on trajectory. I did alot of playing with JBM and I was very suprised to see how much of a change going from normal winter time stats over to summer stats was. But 2" is a very large change. So far, JBM has been correct for me, but I doubt that everything was due to the change in weather. It was more likely a mixture of many things.
2" is quite a bit, but still possible. If it was entirely due to the weather, I couldn't say. But, the weather does have quite a bit impact on trajectory. I did alot of playing with JBM and I was very suprised to see how much of a change going from normal winter time stats over to summer stats was. But 2" is a very large change. So far, JBM has been correct for me, but I doubt that everything was due to the change in weather. It was more likely a mixture of many things.
Re: Weather affecting 100 zero?
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: was21</div><div class="ubbcode-body">Check out a psychrometric chart and you will find out that higher humidity equals lower air density...not higher as stated.
just sayin'
FWIW
</div></div>
Thanks for the tip. I read up on this last night, and was surprised to find that what I had thought was actually backwards.
<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: was21</div><div class="ubbcode-body">Check out a psychrometric chart and you will find out that higher humidity equals lower air density...not higher as stated.
just sayin'
FWIW
</div></div>
Thanks for the tip. I read up on this last night, and was surprised to find that what I had thought was actually backwards.
Re: Weather affecting 100 zero?
I would look elsewhere for the issue. More than likely it's psychological. Changes is weather affect animals quite a bit (and yes, we count as animals). It's one of the reasons I like to shoot matches in the rain and snow. It flat rattles some folks.
I pulled out the ballistic calculator and punched in the data for match (sub-sonic) .22LR. There was no estimated change in impact at 100 yards even with a 2.00"Hg pressure change.
I would look elsewhere for the issue. More than likely it's psychological. Changes is weather affect animals quite a bit (and yes, we count as animals). It's one of the reasons I like to shoot matches in the rain and snow. It flat rattles some folks.
I pulled out the ballistic calculator and punched in the data for match (sub-sonic) .22LR. There was no estimated change in impact at 100 yards even with a 2.00"Hg pressure change.
Re: Weather affecting 100 zero?
It did go from sunny to cloudy. As for it being psychological, there were three of us shooting, so the effect would have had to hit us all. We were shooting out of the same box of ammo, I can't help but wonder if we just hit a bunch of ammo with lower volisity. I know the speed of the ammo varies because once in a while one of the rounds will go sonic and hit above the rest of the rounds in the group.
It did go from sunny to cloudy. As for it being psychological, there were three of us shooting, so the effect would have had to hit us all. We were shooting out of the same box of ammo, I can't help but wonder if we just hit a bunch of ammo with lower volisity. I know the speed of the ammo varies because once in a while one of the rounds will go sonic and hit above the rest of the rounds in the group.
Re: Weather affecting 100 zero?
YES. I experienced this after the TSC match last month. There was some drizzle from a T storm that grazed our location and the air was thick and hot when it wasn't drizzle. I was 2.5 minutes below my normal 57yd setting..puzzling. I shot last Thursday at 50yds and everything was spot on normal. I made a note in my log of the conditions so now if it happens again I know where I should be. I never tried it at 112yds while this anomaly was occuring but I should have. I suppose I could assume 2.5 minute adjustment would be in order accross the course in the conditions I experienced, but that may be incorrect. I was using Federal 922A ammo and all from the same lot I have been shooting.
YES. I experienced this after the TSC match last month. There was some drizzle from a T storm that grazed our location and the air was thick and hot when it wasn't drizzle. I was 2.5 minutes below my normal 57yd setting..puzzling. I shot last Thursday at 50yds and everything was spot on normal. I made a note in my log of the conditions so now if it happens again I know where I should be. I never tried it at 112yds while this anomaly was occuring but I should have. I suppose I could assume 2.5 minute adjustment would be in order accross the course in the conditions I experienced, but that may be incorrect. I was using Federal 922A ammo and all from the same lot I have been shooting.
Re: Weather affecting 100 zero?
armorpl8chikn: Thanks for confirming my findings. I would like to understand what caused this. Is it temperature, humidity, a combination of both? Is it affecting the exterior ballistics of the bullet in flight? Is it affecting the ignition therefore the velocity of the round? Could it be causing the stock to expand or shrink? Could it be a combination of some or all of the items above?
armorpl8chikn: Thanks for confirming my findings. I would like to understand what caused this. Is it temperature, humidity, a combination of both? Is it affecting the exterior ballistics of the bullet in flight? Is it affecting the ignition therefore the velocity of the round? Could it be causing the stock to expand or shrink? Could it be a combination of some or all of the items above?
Re: Weather affecting 100 zero?
IIRC, 1 in 36 shots will hit a rain drop in a moderate rain. This will cause what you describe. I have not tried it, but know folks who have and confirmed it.
IIRC, 1 in 36 shots will hit a rain drop in a moderate rain. This will cause what you describe. I have not tried it, but know folks who have and confirmed it.
Re: Weather affecting 100 zero?
Did it cool off quite a bit when it started raining? My .22 is pretty temperature sensitive with regards to muzzle velocity. almost 2MOA seems like a lot for that alone to account for it, though.
Did it cool off quite a bit when it started raining? My .22 is pretty temperature sensitive with regards to muzzle velocity. almost 2MOA seems like a lot for that alone to account for it, though.
Re: Weather affecting 100 zero?
it did cool off, it also went from sunny to overcast. Mirage may have been a factor. Another question, Do you all have to fine tune your .22's 100 yard zero each trip to the range?
it did cool off, it also went from sunny to overcast. Mirage may have been a factor. Another question, Do you all have to fine tune your .22's 100 yard zero each trip to the range?
Re: Weather affecting 100 zero?
Humidity....nope
Temp....not unless you had to put your down jacket on to keep warm..he-he
Light....you betcha
Humidity....nope
Temp....not unless you had to put your down jacket on to keep warm..he-he
Light....you betcha
Re: Weather affecting 100 zero?
Only 1 in 36 rounds hit a rain drop? Seems like a guy could do better than that. Unfortunately, here in Nevada we don't get a chance to practice on rain drops much.
Only 1 in 36 rounds hit a rain drop? Seems like a guy could do better than that. Unfortunately, here in Nevada we don't get a chance to practice on rain drops much.
Re: Weather affecting 100 zero?
I did notice that my 100yd dope would change a few clicks here or there, but I don't have any records because that was before I started keeping a log. It could just be how I was addressing the rifle differently each time (the scope was mounted high and I was using a chin-weld) or it could have been lighting, or I could have just been shooting poorly.
I did notice that my 100yd dope would change a few clicks here or there, but I don't have any records because that was before I started keeping a log. It could just be how I was addressing the rifle differently each time (the scope was mounted high and I was using a chin-weld) or it could have been lighting, or I could have just been shooting poorly.
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