Range Report Inclement weather and pressures

[Unknown]

Another shooter was asking me if inclement weather can raise pressures. I think everyone knows that hot weather raises pressures if it is over your normal met/env conditions, and that colder weather lowers pressures.

The only factor I could think of that might raise pressures is having wet ammo in the chamber, in which case the brass couldn't expand properly, or having water droplets inside the barrel. Neither condition seems as safe as I would like, but the question wasn't about safety as much as how the change in pressures would effect accuracy and trajectory.

On another note, I have always believed that shooting in a heavy rain downpour where the raindrops are the big fat ones, (not a light misting or drizzle) will adversely effect both accuracy and trajectory. It just seems to make sense that if the bullet has to blast it's way through 50 or 100 raindrops each weighing .1 gram, that it will hurt accuracy.

Of course, maybe I just shoot worse on days where the weather is really crappy...this is the Pacific Northwest, and contrary to what you may have heard, it does rain here occasionally.

Is there any research on this?

 

[kraigWY]

Re: Inclement weather and pressures

Inclement weather effects the shooter, not the gun & ammo.

The biggest problem in shooting in inclement weather is we don't practice in inclement weather. We set by the fire then when something comes up, we can't do it so we want to blame the enviorment.

 

[Unknown]

Re: Inclement weather and pressures

KraigWY,
That is what I thought. Because I live in the northwest, I regularly practice in rotten weather. The Marine Corp helped break me of worrying about shooting while laying in a puddle, or some mud. Between my willingness to shoot in rotten conditions, and knowing that I won't die if I get wet at a match, I think it gives me an advantage over the "fair weather" shooters who waste time looking for a dry place to lay down in a rain storm.

A younger shooter had asked me the question about weather effecting the accuracy and trajectory, and you are confirming my initial suspicions...it is the shooter that is effected, not the weapon system (higher and lower temperatures than your normal meteorological/environmental conditions excepted).

Of course, if anyone shoots with a barrel bore full of anything (water, mud, damn near any obstruction) a change in accuracy or will be the least of your problems. The pressures then will most likely blow up a rifle..

 

[LRS_Ranger]

Re: Inclement weather and pressures

Haha, you got it posted before me... As far as the external ballistics, I remember reading in "Understanding Firearm Ballistics" that in testing by the US Army at Aberdeen, most rain does not affect accuracy at all. I suppose that in a complete Amazon downpour it might at longer ranges, but then you wouldn't be able to see that far to make the shot anyway.

Internally, I'm guessing that if anything, extra water in the chamber could raise pressures by filling up any airspace around the cartrage. I was wondering because I was reading a thread some time ago where someone was saying that one of their loads worked really well, but in nasty weather would start showing pressure signs. I wasn't getting pressure signs, but since I was running a hotter load in the driving rain, it made me wonder... Thanks for taking the time to weigh in..

Most of my groups were nothing to write home about, but I attribute that to bairly seeing the target... good times!

 

[Unknown]

Re: Inclement weather and pressures

I was out shooting last week, and all my rifles sucked...even rifles that are always accurate..There is no reason that a TRG22 shooting ammo from the same lot that performs well other times shouldn't shoot well. I just figured I was having an off day because everything was soaking wet, the wind was blowing so hard it actually blew my 5x5 foot target mounting backers out of the frames 3x. Rain was those huge fat drops, coming down at about 20 degrees from the wind...

I'm sure it was my bad day shooting because all the rifles shot poorly.

 

[wadebrown]

Re: Inclement weather and pressures

I believe rain's biggest effect on accuracy is due to reduced visibility, if the rain is too heavy to see the target it is pretty hard to hit it.

I did some testing on a wind measurement system with the gun on a machine rest bedded in a lot of concrete. The wind measurement system would spit out a wind profile and we would input that into the ballistics solver. The gun was zero'ed at the beginning of the day and was not touched the rest of the day. We tested it in the rain and the gun was still hitting where we thought it would at 1,000 meters, even though I could not see the the target looking through a Leupold Mark IV spotting scope. That test showed me that the biggest limiting factor when shooting in the rain was the shooter's ability to see the target.

I love shooting in a light mist as it is a great wind indicator, almost as good as when the dogwoods are in bloom. I used to shoot every Saturday morning in whatever weather Saturday offered so I was forced to shoot in all weathers. My reasoning behind shooting in all weathers was that hunting is done in all weathers.

wade

 

[Unknown]

Re: Inclement weather and pressures


I love shooting in a light mist as it is a great wind indicator, almost as good as when the dogwoods are in bloom. I used to shoot every Saturday morning in whatever weather Saturday offered so I was forced to shoot in all weathers. My reasoning behind shooting in all weathers was that hunting is done in all weathers.

wade [/quote]

Very sound reasoning. That is the same reason I practice regardless of how lousy, or cold the weather. I can only control myself...(barely). I most certainly can't control the weather, so I might as well try and reduce as many variables that hurt precision as I can.

 

[ChadTRG42]

Re: Inclement weather and pressures

Another factor that WILL effect your ammo, is firing a round that is wet. If you chamber a round that has moisture on the outside of it, it will increase pressures. If there is a lot of water on it, you can easily blow primers with ammo that shows no pressure sign when dry. I have seen this happen at shooting matches when it's raining, and when testing loads that were fine when dry. These higher pressures can effect the velocity and can easily change up your load and/or point of impact.

 

[armymedic.2]

Re: Inclement weather and pressures

good point on the wet ammo, never saw it myself but it makes sense.


yesterday i was shooting in 100% humidity as it had just stopped snowing (and my kestrel told me so), and my elevation adj was not impacted at all @ 800 yards compared to my 50% hum. zero.

will that moisture in the air create those same high pressures? is that why poi is supposed to rise? esp if it causes condesation on the bullets?

interesting stuff.......

 

[USAF1A8]

Re: Inclement weather and pressures

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: armymedic.2</div><div class="ubbcode-body">is that why poi is supposed to rise?
interesting stuff.......</div></div>

i remeber someone here posting not too long ago on a similar question. Not saying it wont affect the pressures internally as well, i just dont now. What he offered up was something to the effect of: Ever driven by a pond or lake early in the morning just as the sun was hitting it, ever seen the mist that rises from the surface? He explained that that phenomenon is why the POI shifted up. I suppose that he meant that humidity in the air tends to rise, so it deffinately affects POI. I would think any moisture in the chamber could have that effect too, but to how much of an extent?

Made sense to me, I can remember driving past the Naval Post Graduate school in Monterey hundreds of times and seeing that phenomenon, just never applied it to shooting. These weren't exactly warm mornings either so i wonder st what temps, if temps have an effect, this is part of the equation.

 

[Lindy]

Re: Inclement weather and pressures

Humidity has a very small effect on POI at ranges of 1000 yards or less. To confirm that for yourself, set up a ballistic program with a load, then look at the effect of changing the RH from 0 percent to 100 percent.

Unless I'm shooting way beyond 1000 yards, I just set the RH in my ballistic programs at 50 percent and leave it alone. The maximum possible error then is about half of what the max effect of going from 0 to 100 percent.

A ballistic program is a great tool for experimenting to see what does or doesn't matter with respect to ballistics, both internal and external.

 

[Unknown]

Re: Inclement weather and pressures

The water on ammo was one of my initial thoughts. It just makes sense that if the water on the outside of the cartridge case prohibits the case from expanding properly on firing, that pressures will go up...way up.

Humidity IS a factor in trajectory. That is why the exbal program asks for barometric pressure, altitude, and humidity, temperature are required (among other things) in order to generate a trajectory arc.

 

[armymedic.2]

Re: Inclement weather and pressures

yeah i got to go with lindy on this one....humidity is a factor (to me and my shooting) like spin drift is a factor.

in other words, from the shooting that i can do (skill level), at the ranges i shoot at , 1000 and less, i can't see it making a noticeable diff

BB - i know just what you are talking about, i think that has more to do with the temp of the water being slower to cool down than the air, and this causes some "lift off". air cold, water warm= heat rises, just my guess.

 

[Tribe]

Re: Inclement weather and pressures

Unknown, I am a wet sider. Externally, I have never noticed any difference whatsoever.

Internally is a whole 'nother factor... Shoot with moisture on the ammo/in the chamber, and you will see significant pressure spikes, relative to the amount of wet... which of course, should somewhat flatten your trajectory... and thus throw off your dope.

I had a load that I was very fond of... it was hot, but gave me no pressure signs under mild conditions. Shot it in sideways rain, where it was impossible to keep anything dry.... blew a bunch of primers that day. Lesson learned... went to a mild accuracy node... haven't had the problem since... may still see increased pressure, but there's always the follow-up... and I'm still running.

 

[USAF1A8]

Re: Inclement weather and pressures

right im with you medic, just an interesting illustration for me was all. Enter always with mind open/mouth closed- serves me well, thanks for the explanation

 

[Unknown]

Re: Inclement weather and pressures

Tribe,
I'm on the wet side in Oregon, so our weather is pretty much the same. I think the biggest variable in this would be having water droplets on the outside of the cartridge case, or between the cartridge case and chamber walls. This water would prevent the case from expanding properly, thereby causing higher pressures.

I wonder if it would also cause the same sort of problem that oil on the cartridge case does? When there is oil on the case, or inside the chamber, the case can't grip the walls of the chamber properly, and causes higher rearward bolt thrust.

 

[LRS_Ranger]

Re: Inclement weather and pressures

Looking at the brass that I shot that day, every single one has ejector slot marks on the case head. When I went to reprime, some of the primer pockets were looser than normal as well. This happened on even the milder loads as well. So something did definitely happen to send my pressures up. I guess the jury is still out on what that was, but my money is on water in the chamber area keeping the case from expanding properly...

 

[WDL]

Re: Inclement weather and pressures

POI shift was mentioned a few posts back. In particular, in the morning as mist was observed rising off a pond. Actually what you are seeing is a temperature inversion. And this causes the light rays to bend. So when it appears that the POI has shifted up, actually the POA has shifted up, causing the POI to rise.

 

[winxp_man]

Re: Inclement weather and pressures

<div class="ubbcode-block"><div class="ubbcode-header">Originally Posted By: Lindy</div><div class="ubbcode-body">Humidity has a very small effect on POI at ranges of 1000 yards or less. To confirm that for yourself, set up a ballistic program with a load, then look at the effect of changing the RH from 0 percent to 100 percent.

Unless I'm shooting way beyond 1000 yards, I just set the RH in my ballistic programs at 50 percent and leave it alone. The maximum possible error then is about half of what the max effect of going from 0 to 100 percent.

A ballistic program is a great tool for experimenting to see what does or doesn't matter with respect to ballistics, both internal and external.

</div></div>


+1 humidity for ranges under 1000 yards will not effect the bullet much. Barometric pressure on the other hand will. I have seen this while I was shooting.

 

[Hellbender]

Re: Inclement weather and pressures

What you are seeing with the wet cases, is not changes in internal pressure of the case, it is the case not expanding to grip the walls of the chamber properly.

This allows more of the available pressure to push rearward on the bolt, giving signs of excess pressure, just like an oily chamber.

Here is a neat study where he polished the chamber with different grits of sandpaper, from a rough finish to a mirror finish and the resultant changes on the case head/bolt thrust pressure.

http://www.varmintal.com/a243z.htm

A low friction chamber (polished, oil or water) can be over 8000 lbs compared to a normal chamber having 2500-3000 lbs of bolt thrust.