Shooting in the rain

[jkajfes]

High humidity, temperature, or altitude makes air less dense. Low humidity, temperature, or altitude results in denser air.

To illustrate how air density can effect us there is an interesting story concerning air density which occurred here some years ago. A small twin engine aircraft left Las Vegas at 2200' and a temperature of 82F and landed here at seal level at a temperature of -45C. Upon landing the tires on both sides of the plane went flat and there he was, stuck on the runway. His tires were nice and hard in the warm air, but the air in his tires became denser in the cold air at sea level, therefore took up less space, resulting in flats. For those knowledgeable about aircraft, it is not clear if the tires were originally inflated with nitrogen, but I doubt that they were.

A supersonic bullet passing through rain may-not be effected by the water drops it passes through due to it's shock wave, but when shooting in the rain our ammunition get wets, and wet ammo results in a different point of impact than dry ammunition. Water is not compressible, so it follows that a wet cartridge will result in higher pressure than a dry cartridge because the wet cartridge takes up more space in the chamber.

ya and that's why many of us ##### moan and groan on wet shoot days. Trying to keep a tight chamber from water getting in, water on the bullets and cases and water possibly in the muzzle if your not damn careful..

Depending on the type of down pour I have noticed it get very calm at Mons for example before the #### hit's the fan... during this time you can get some nice zeroes.... but you need to remember as mentioned the thin air dense air thing.

 

[Ardent]

For real?

Yes, for real, ice doesn't have the same density as liquid water either for reference... that's why it floats in your glass. The three states, solid, liquid, and gas, are distinct physical forms of a chemical compound and not just "water". Water vapor, like the ice, is every bit as different from liquid water, it's not just "misty" water, it's a completely different arrangement of molecules in the form of a gas. This gas is less dense than air. When you "feel" the humidity such as seeing your glasses fog up, you're experiencing condensing water vapor, it's not actually "water" while it's in the air only once it condenses into a liquid.

 

[jake2]

I'll through this out there.
It has been my experience that the Point of impact will actually go UP in heavy rain. This is due to the increased chamber pressure. I can look at my once fired brass and tell whether or not it was raining heavy that day. There will be a small brass "boss" where the brass flowed into the bolt ejector hole. This is what causes some bolts to be difficult to open in an overpressure situation.
I have some loaded ammo that was great on a clear day. In one competition, in the rain, I started blowing primers. That was the only ammo I had and had to borrow some to complete the match. Another competitor offered to lend some handloaded ammo he said was good but his charge was larger than mine using the same calibre, bullet and powder. I declined going with a friend's commercial match ammo. I'm glad I did because the other competitor had to withdraw from the competition because his ejector hole was full of brass and would not eject the rounds not to mention also blowing primers.

Keep this in mind when you are using a ammo lot that you know or suspect is on the edge of being overpressure. Shoot in a downpour and you'll quickly discover this.

 

[shoot44]

I read in Precision Shooting magazine 10 yrs ago or so about some guy who did a test by shooting groups with a 6ppc bench gun through a sprinkler and without the sprinkler and the groups were the same. He concluded that rain does not effect bullets in flight. Different density altitude however does effect groups. Search on benchrest.com for posts about density altitude. Its interesting.

 

[Terry Perkins]

I have some loaded ammo that was great on a clear day. In one competition, in the rain, I started blowing primers.

This sounds like water droplets on the cases or in the chamber. Pressure will rise significantly because the water does displace a certain amount of volume that is needed for case expansion.

 

[jake2]

This sounds like water droplets on the cases or in the chamber. Pressure will rise significantly because the water does displace a certain amount of volume that is needed for case expansion.

Yes, that is what is happening but in a downpour, out in the open, during a match, it is hard not to get water on the cases and inside the chamber.

This is not to say that shooting in the rain is a safety concern but it something to keep in mind and like I said it is my experience the increase in pressure overcomes the environmental issues and throws your shots high.

 

[NormB]

I'll through this out there.
It has been my experience that the Point of impact will actually go UP in heavy rain. This is due to the increased chamber pressure. I can look at my once fired brass and tell whether or not it was raining heavy that day. There will be a small brass "boss" where the brass flowed into the bolt ejector hole. This is what causes some bolts to be difficult to open in an overpressure situation.
I have some loaded ammo that was great on a clear day. In one competition, in the rain, I started blowing primers. That was the only ammo I had and had to borrow some to complete the match. Another competitor offered to lend some handloaded ammo he said was good but his charge was larger than mine using the same calibre, bullet and powder. I declined going with a friend's commercial match ammo. I'm glad I did because the other competitor had to withdraw from the competition because his ejector hole was full of brass and would not eject the rounds not to mention also blowing primers.

Keep this in mind when you are using a ammo lot that you know or suspect is on the edge of being overpressure. Shoot in a downpour and you'll quickly discover this.

I don't think the volume of water on the case can change the volume in the chamber that much that would give signs of high pressure ie. blown primer and flattened and expanded bases and extraction grooves.

But these do exist in the rain.

What I think is happening is the water/steam is acting like a lubricant and not allowing the case walls to stick to the chamber and reduce the rearward force. Thus all the pressure is taken by the back of the case. Extraction grooves are crushed and expanded, primers are pierced, and these cases won't fit in your shell holder anymore.


Also when shooting in the rain with a head wind, a drop of water can sit in the muzzle. When the bullet hits this basically incompressible drop, it can give a "rain shot", a wild usually high shot.

NormB

 

[pazzo]

humidity doesn't play nearly the deciding role that barometric pressure or elevation/ temperature does.

go to JBM and see for yourself. find your bullet, punch in the appropriate info that corresponds to your shooting location, and see what the humidity reads. from 0% - 100% humidity the bullet (.308 Sierra HPBT MatchKing) only drops a couple of inches (at 1000 yds). it's best to just always leave it at 60%.

now the drop when at sea level compared to say 3000' is a different issue (difference of ~3 MOA @ 1000 yds (when at 15 deg celsius)), let alone 0 degrees celsius compared to 35 degrees celsius (difference of ~3.5 MOA @ 1000 yds (when at sea level)).

and it's pretty safe to leave the barometric pressure at the 29.92 in hg. (which is the default setting), given that it is a fairly stable reading for most areas (except on top of a mountain while snowing, or in a rain cloud).

 

[horseman2]

Shooting a 22-250 in heavy rain and the occasional "Puff of Steam" could be seen. Do not recall the accuracy as the paper targets were mushy.