Advanced Marksmanship Shooting in the rain POI question

bm11

bm11

Gunny Sergeant
Full Member
Minuteman
Jun 18, 2010
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Maine
#1
Shot in the rain for the first time today. With a slight sprinkle, I noticed no effect, but when it started raining, I noticed a 1 moa difference in POI, both at 100 yards and 230 yards.

Is this typical? Or is it variable based on how hard it is raining?
 
#3
Re: Shooting in the rain POI question

Just make sure you don't get any water in the barrel. At Bisley last year, we shot in the rain nearly every day. During the team match, in a rather heavy downpour, one of our guys fired a round that almost missed the target low at 1000 yards. We should have run a patch through the barrel first.
Also, be careful not to get your ammo wet or any water in the chamber as this can cause high pressure spikes.
 
#4
Re: Shooting in the rain POI question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: CAT5</div><div class="ubbcode-body">I have never noticed any effect from it, even at long range. </div></div>Hmmn, I'll evaluate the scope mount then, as I had moved my scope .25 inches forward that morning and re zeroed.
 
#5
Re: Shooting in the rain POI question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: DGosnell</div><div class="ubbcode-body">Just make sure you don't get any water in the barrel. At Bisley last year, we shot in the rain nearly every day. During the team match, in a rather heavy downpour, one of our guys fired a round that almost missed the target low at 1000 yards. We should have run a patch through the barrel first.
Also, be careful not to get your ammo wet or any water in the chamber as this can cause high pressure spikes. </div></div>Thank you for the advice. My range has a sheltered shooting platform so it wasn't an issue, but I did clean my rifle after because due to wind, it did get a little wet.
 
#7
Re: Shooting in the rain POI question

My understanding (supported by my experience shooting here in the PNW) is that the precip falling in the air has no effect -- just dope for the humidity.

HOWEVER -- water in the chamber can mess with pressure (especially important to note if you shoot right at pressure limits in wet weather). Not sure what a bunch of precip further down the barrel would do...
 
#8
Re: Shooting in the rain POI question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Willys46</div><div class="ubbcode-body">which direction was the MOA shift. I have found that I shoot a little high during the rain.

I love shooting in the rain. you can really see the wind well. </div></div>Shift was down.
 
#9
Re: Shooting in the rain POI question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: mattj</div><div class="ubbcode-body">My understanding (supported by my experience shooting here in the PNW) is that the precip falling in the air has no effect -- just dope for the humidity.
</div></div>Wouldn't rain falling create additional resistance in the air causing the bullet to slow faster than in non rain conditions, causing more drop per distance shot? Or does the dope for humidity handle that? I don't have a ballistics calc, if you don't mind plugging in the dope for humidity in the rain vs dry at 230 yards? (.308) I checked my scope mount screws and they hadn't loosened, and the scope doesn't have any marks from walking.

Thanks,

-Bob
 
#10
Re: Shooting in the rain POI question

Have never noticed a difference in dope due to rain--and that was shooting to 800Y (couldn't see beyond that). Related, I have never seen a change in my dope due to barometric pressure changes from passing fronts, either (big fronts--like pre-hurricane level drops and winter storms while the winds were still steady).

I don't think AI is water sensitive at all, but I am usually firing suppressed and at a rate that will keep the barrel dry. That said, I've had heavy rain streaming off the scope and over the action with no change in POI. The rifle keeps chugging and is totally consistent--its shoots the same (adjusting dope for temperature) from -20 to +110 regardless of snow, sleet, or rain in the action. If you want to see what your AI and S&B were for, take them out in freezing sleet and shoot. You will gain a whole new respect for the designers.

Regarding your other question--I'd suspect the high pressure wave forming in front of the bullet while in flight would displace any raindrops.

 
#11
Re: Shooting in the rain POI question

Perhaps I need to double check the torque on my mount and ring screws then.


Can't wait to get this rig out in the winter either, by the way. We get a ton here in Maine, can't wait to see what this is all about.
 
#13
Re: Shooting in the rain POI question

Light's up, sights up. Light's down, sights down. I think you're seeing a lighting issue.

I <span style="font-style: italic">seriously</span> doubt that heating/cooling effects on sight mounts would be even measurable without sophisticated equipment. Look elsewhere for significant influences.

The points we need to understand about the magnitude of random environmental influences is not so much about how much each one impedes consistent POIs, but how much they all affect accuracy, and how small a part in the sum total any single one constitutes. It's like the piccolo flubbing a note in the middle of an orchestratic crescendo. You might notice the effect, if you have a trained ear, but most of us are simply overwhelmed by the totality.

Newguys are fascinated with the knowledge that applies to consistent accuracy. They tend to take the individual parts somewhat out of context with the whole, and also tend to assign rather more importance to the individual items than many of them will warrant.

It still boils down to applied basics, reliable equipment and ammunition, and practice that discloses <span style="font-style: italic">their</span> rifle's performance under all conceiveable conditions, and <span style="font-style: italic">their</span> personal competence with firearms in general.

By all means explore the details, but <span style="font-style: italic">master</span> the basics first. I'm <span style="font-style: italic">still</span> working on that part.

Greg
 
#14
Re: Shooting in the rain POI question

The air dam around your bullet prevents the rain from having any real effect, BUT, a downpour will give you some good water drops on your crown/in your muzzle...
 
#16
Re: Shooting in the rain POI question

Hey guys,

Thanks for the comments. I had the opportunity to shoot in the rain again the other day, even in a downpour, and there was no shift in POI. I have no idea what was causing it the other day.
 
#17
Re: Shooting in the rain POI question

was there any mirage before the rain?
if so then the rain will kill the mirage and shift poi down

but this is just an optical illusion not a true shift
 
#19
Re: Shooting in the rain POI question

In service rifle&across the course comps, we use a "light up,sights up light down,sights down" principile. Bright sunlight and overcast conditions affect the sighting picture diffferantly.
 
#20
Re: Shooting in the rain POI question

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Etype</div><div class="ubbcode-body">The air dam around your bullet prevents the rain from having any real effect.</div></div>
I think this is it. Will run it past my aerospace guy.
 
#21
Re: Shooting in the rain POI question

I know from ground school that the moisture in the air is less dense than dry air. H2O is a lighter molecule than other typical gases. I wondered what impact rain would have on ballistic trajectories. Good discussion.
 
#22
Re: Shooting in the rain POI question

I have found that rain/fog/mist affect the way I perceive my sight picture, not unlike low light shooting. The image presents with less brightness and often, a lot less contrast, as well as diminished color intensity.
Extra care at properly aligning the target with the reticle gives results consistent with normal visibility shooting.
 
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