Shooting in the Rain?

[beezaur]

Hi Guys,

What effect does shooting in the rain have on bullet flight?

I took a shot at my 500-yd target this morning in the rain, and it hit about 1.5 MOA low. This is a .243 Win game bullet (Remingtom 100-gr PSPCL) at ~3050 fps off a bipod. The load gives around 1/2-3/4 MOA accuracy. I had been whacking the target regularly at the same temperature. Barometric pressure was 0.5 inHg lower today, I had a 10-mph crosswind, and it was raining -- those were essentially the only changes.

I guess what I am wondering is whether a guy can reasonably compensate for rain. I have never bothered to try any precise shooting in the rain, so this is new to me. Any help is appreciated.

(I have some Berger 95-gr VLDs, but my handloading setup is still mothballed from 10 yrs ago -- will get back to that soon.)

Scott

 

[LB]

The problem is to quantify "rain". Enough rainfall and you can't see past a certain distance though the scope. Too many magnified sparkles. I'd guess you should readjust your parameters. A sunshade helps to keep water from beading on the objective but it's the other end that really messes with your ability to see clearly. I think that if the air density is greater, then you would experience more drop, how significant, can't say?

Good hunting. LB

 

[Buffalobob]

JB1000Br would know something about this as would almost any of the Williamsport 1000 yd shooters being as the last match was held in the rain. Maybe he can give you some insight.

 

[Charles A]

I'm not JB, but I do get paid to shoot "things" LR all over the world under any condition, and besides the MET effects, have not noticed any POA/POI differnces caused by the rain. The shooters I work with agree.

 

[Michael Eichele]

Trust me it rains alot in AK. Some places here are measured in feet and not inches for anual rain fall. I havent ever noticed a POI shift due to rain. Its normally temprature and barometric pressure changes that would move your POI that much at that range. Also, was your ammo colder than normal??

 

[jb1000br]

have shot some good groups in the rain...snow...and even hail a year or two ago...240's made it thru the hail pretty well at Williamsport /ubbthreads/images/graemlins/wink.gif

i agree, no affect that i have seen yet...

Was it the first shot from a clean bore?

JB

 

[Eaglet]

jb1000br,
Have you folks ever thought about the possibility that once a bullet is above certain speed, it's eventually in a different dimension? /ubbthreads/images/graemlins/ooo.gif, well you might think it's stupid but throw a base ball in a heavy rain, that ball is wet before is caught, right? and all those little bitty drops hitting it from above have to cause some effect, right? I bet if you could catch a bullet flying over let's say 2000 f/s in extreme rain it wouldn't be wet... Well crazy or not it's interesting... /ubbthreads/images/graemlins/confused.gif But if it was in a different dimension how would it kill a coyote that is in this dimension... /ubbthreads/images/graemlins/confused.gif Well... who knows why it's not affected by the rain... /ubbthreads/images/graemlins/frown.gif /ubbthreads/images/graemlins/grin.gif /ubbthreads/images/graemlins/crazy.gif /ubbthreads/images/graemlins/wink.gif /ubbthreads/images/graemlins/smile.gif

 

[4ked Horn]

[ QUOTE ]
throw a base ball in a heavy rain, that ball is wet before is caught, right? and all those little bitty drops hitting it from above have to cause some effect, right? I bet if you could catch a bullet flying over let's say 2000 f/s in extreme rain it wouldn't be wet...

[/ QUOTE ]

That baseball ain't spinning at 200,000 RPM and flying through a sonic shockwave either. Yes the bullets are kissing the spirit world alright.

(Hey I just noticed something. This is my thousandth post. Well whada ya know? /ubbthreads/images/graemlins/laugh.gif)

 

[Eaglet]

Forky,
I'm sure glad I contributed some how to that 1000th post!!! /ubbthreads/images/graemlins/cool.gif /ubbthreads/images/graemlins/laugh.gif /ubbthreads/images/graemlins/smile.gif

 

[beezaur]

[ QUOTE ]

Was it the first shot from a clean bore?

JB

[/ QUOTE ]

Doh! That was it. Color me stupid.

Actually It was the first time I cleaned a bore in years after being busy with other things like school and then work. I guess I'm a little rusty. Oops.

The lack of effect actually makes sense to me. If you figure time of flight on a long shot is something like one second, then the bullet would have to hit a raindrop during that time in order for the rain to have any effect at all. Otherwise the bullet is just flying through damp air, which is known to not be a problem.

You could get a rough idea of the probability of the bullet hitting a drop by exposing something like a piece of paper to the rain in question for a time equal to the time of flight. So you expose your paper for one second or so, and you only get a few drops on the paper. The probability that the bullet will hit a drop is almost the same as the probability that a bullet-diameter circle drawn randomly on that paper will touch a raindrop. Pretty slim odds.

I would still think if the bullet did hit a drop there would be some deflection, especially if the hit was early on in flight. There has to be a major impulse from turning whatever mass a raindrop is into vapor.

Scott

 

[Eaglet]

beezaur,
You just got too complicated for me. /ubbthreads/images/graemlins/smile.gif

 

[Buffalobob]

I told you JB would know something.

Here are the details of a calculation that I did on another forum on the same question. Missing from the calculation is the effect of "glancing blows" from raindrops on the stability of the bullets and the lowering of BC from yaw caused by such a glancing blow. Nor did I include that fact that raindrops are a liquid and will deform on impact which will tend to lessen any effect of the collision,(if you have ever done a belly buster off a diving board you know that water is not "soft").

For those who wisely chose not to wade through the calculations here is the bottom lines.

The amount of rain from the nearest rain gauge on the last light gun match at Williamsport was only 0.32 inches over about a four hour period. It will normally rain once a month a hard rain of 1.0 inches in the eastern seaboard states. A hurricane will drop about 10 inches of rain. My calculations say you would need the amount of raindrops in the air that comes from a hurricane to affect bullet path at 100 yds. For a thousand yards you would need it to be raining about ten times as hard as it was the last match at Wiliamsport.

For the non-geeky people, a good rule of thumb is that if it is raining so hard that you cannot see the target then you will need to shoot high. /ubbthreads/images/graemlins/confused.gif

For all of you fellow geekies here is something to criticize:

mass of a raindrop is about 0.008 grams and falls at a speed of 8 m/sec. Momentum is about 0.064gm/s

150 grain bullet at slightly over 3000fps give the following momentum.

At 15 grains per gram then bullet mass is 150 divided by 15 = 10 grams

Velocity is 1000m/sec

Momentum is 10 grams times 1000m/s = 10,000g/ms

collision impact of one raindrop with one bullet is
10,000gm/s + 0.064 gm/s

You would need to hit 150 rain drops in 100 yards to get a 1% deflection. This would be one drop every 18 inches

I may have missed a conversion factor but I think this is a rainfall event of 10 inches per hour (about what you get with a hurricane). So when your bullets start striking low at 100 yds in a rain you really should be shooting from your boat and have your PFD on and next time do not ignore the evacuation order.

On the other hand if you are shooting at 1000 yds you definitely are going to be a significant amount low when you have a "good rain" not a drizzle but a nice steady rain. I question whether you could see the target at 1000yds in the amount of rain needed to cause a low strike.

 

[Eaglet]

buffalobob, /ubbthreads/images/graemlins/smile.gif
Did I in any way help to inspire you to write such fine post? /ubbthreads/images/graemlins/blush.gif

 

[jb1000br]

The rain drops are vaporized before they can get to the bullet...as long as it is supersonic...

Glad I could be of assistance /ubbthreads/images/graemlins/wink.gif