How much can heavy rain affect long range ballistics?

[hartzpad]

I went shooting the other day with my VEPR rifles on a 100 yard range. It started pouring rain about 1/2 way through, but I just kept on shooting. I was talking with my gun noob friend later in the day and he asked me how much heavy rain would affect the bullet in shooting. I had never considered it. I would suppose that at 100 yards you would never notice a difference, unless it was hailing so large and so hard that the projectile would be certain to contact a hail ball. But, at longer ranges, I would suppose that heavy rain would have a definite effect on the ballistics of the projectile, at least affecting its path or velocity, because water and raindrops do have a significant mass. Look at what happens if you shoot into a pond, the projectile is slowed down within 10 feet of the water.

Any real world experience with how heavy rain affects accuracy and ballistics?

 

[Bacchus]

Great question. I've often wondered the same thing, although I think that there are additional factors (beside raindrops) that might account for differences, such as the change in humidity and resultant disappearance of mirage.

 

[WT]

Robert Rinker, in his book "Understanding Ballistics" says that rain has little or no effect on bullets. He references work done by the US military as his source for this view.

 

[Bacchus]

But what about changes in humidity, especially if they occur quickly, like a storm moving in unexpectedly?

 

[mete]

I shot a metallic silhouette match with my 44mag but at one point it rained so hard I couldn't see the 200 yd target !!!

 

[CannibalCrowley]

I still go by what our PMI told us during bootcamp: "rain affects the shooter, not the bullet."

 

[WT]

Certainly, humidity does have an effect on a bullet as does altitude, wind, and temperature. However, raindrops do not have any effect.

 

[Mikul]

Humidity has no effect on a bullet's path as long as the temperature and barametric pressure remain the same.

As to the original question, I have always heard that "Bullet don't fly in the rain," although it seems very counter-intuitive.

 

[benEzra]

Probably has to do with the fact that an object as small as a bullet is rarely going to actually hit a raindrop. From the bullet's perspective, the raindrops are almost stationary, and even in a heavy rain the drops aren't packed particularly close together compared to a 0.3 inch bullet.

 

[taliv]

I dont' know, of course, but I strongly suspect that it's simply a matter of very slim odds of your bullet actually encountering a drop of rain.

if you consider that a "heavy" rain may drop 1" of rain in an hour, that means that the VAST majority of space between you and the target is still air and not water.

at 100 yrds, I'd guess the odds are your bullet hitting a drop of rain are about like winning a small lottery. at 1000 yrds, the odds would be 10x better.

on the off chance your bullet does hit a drop, I think the effect would still be minimal, much less than hitting a twig with a deer rifle.

of course, that's concealed by the fact that your glass and barrel, arms, face, etc are being pelted with rain.

humidity does have a minimal effect. bullets shoot ever so slightly faster when it's more humid. range cards like the ballisticards won't show data for humidity changes though, as it's basically to slight to bother with.

 

[30Cal]

If it's raining hard enough so that you cannot see the target, you may have problems with rain deflecting your shots. Otherwise, I wouldn't sweat it.

If you take a flip through FM 23-10 (sniper field manual) it says to add 1 MoA for every 20% increase in humidity. It also says to add 1MoA for every 20 degree drop in temp. If it's raining out, I toss another 1/2MoA up to my zero (plus any correction for change in temp).

Ty

 

[strambo]

Humidity has no effect on a bullet's path as long as the temperature and barametric pressure remain the same.

Humidity always has an effect. Humidity is the amount of moisture in the air and water vapor is less dense than dry air. Therefore, if the humidity is high (air less dense) than a bullet will have less drag. Dry air=more drag.

Temperature and pressure also have effects, but if they are the same...humidity will still play a part. For example a bullet shot in Houston TX at sea level (STD pressure 29.92) at 85 deg and 100% humidity will have a flatter trajectory than the same bullet shot in the Sahara at sea level (bar 29.92) and a temp of 85deg with 20% humidity.

FM 23-10 (sniper field manual) it says to add 1 MoA for every 20% increase in humidity

I just checked my copy...that's what it says but it is wrong. An increase in humidity makes the air less dense so if it goes UP 20% you better SUBTRACT 1MoA in order to hit the target. This is a common mistake because we use terms to describe humid air as "thick" etc.. however, humid air is actually "thinner" due to the high water vapor content.

Bottom line, rain no problem, but make sure to account for the high humidity and expect a flatter trajectory than normal.

 

[taliv]

right, strambo.

this page explains it well.

even so, 1MOA for 20% humidity seems like a whole lot. I don't think it's anywhere near 1MOA.

i just checked this calculator and it shows that a change from zero humidity to 100% humidity results in a bullet drop at 1000 yrds of -294.9 to -293.3 inches.

I don't have any way to verify that, but a miniscule inch and a half is inline with my previous expectation. I'll check some more ballistic calculators and if any turn up different, I'll update this.

 

[Gunpacker]

Raindrops can be hit

I have shot a lot of matches in rain, and I will state emphatically that raindrops can be hit. I have seen it often. Raindrop turns into a small puff of dense water vapor that looks like puff of smoke for a second. I have never seen proof that it adversely affects accuracy, but can't state for sure. I do know that in a long range rifle match at metallic silhouettes at 2,3 and 5 hundred yards, we were able to hit the targets about as normal. This was not as definitive as a paper grouping might be for determination, but is just an observation. You would think that it would affect the bullet at least minimally, but better tests than mine would have to be conducted. Who wants to do it. Not me. I will just shoot in the rain when I have to and let nature and physics take their course.

 

[4v50 Gary]

Great question and

Thank you Gunpacker for an interesting post. Guess the FM is true.

I can give you the 15-16th Century perspective. It will wash the demons off that cause the ball to be inaccurate.

 

[rayra]

As military pilots like to say 'Big sky, little bullet'.
I would think it would be VERY long odds that your bullet would strike a raindrop in flight.