How much does rain or snow affect ballistics?

[Offfhand]

Assuming a comfortable temperature, and you're shooting under cover, a light, straight down drizzling rain is ideal for testing rifles for accuracy because it is a constant condition. However, having said that I have observed hard rain obviously having an effect on the flight of bullets. That was at the NBRSA national championships, held at St. Louis a few years ago. We were at the 100 yard stage with unlimited class rifles when a sudden downpour hit. Unlimited class benchrest rifles typically shoot extremely small 10 shot groups at 100 yards, so the effect of the dense rain was easy to see and it was considerable. Even considering the effect of wind accompanying the rain, they were many wild shots on our targets that were otherwise unaccountable except for the rain. Some of the world's most experienced and knowledgeable shooters were at that match and had no other explanations for their greatly enlarged groups..

 

[taliv]

http://forum.accurateshooter.com/threads/effect-of-rain-on-accuracy-at-100-yards.3864243/page-2

If we assume a light rain (2.5mm/hr, 2mm diameter raindrops traveling at 6.5m/sec = 23.4e6mm/hr), the volume of a single raindrop is 4.1mm^3, and the number of raindrops in a column of air 1mm^2 at the base * 1hr tall can be calculated as 2.5mm/hr / 4.1mm^3 = 0.61. The density of raindrops in the air is, therefore, 0.61/23.4e6 = 2.6e-8 raindrops/mm^3. The volume of a 6mm bullet's path over 100 yards (= 91m = 91000mm) is pi*3mm^2*91000 = 2.6e6mm^3. On average, then, there are 2.6e-8 * 2.6e6 = 0.07 raindrops in the bullet's path. Put another way, there will be a raindrop (or at least part of a raindrop) in the bullet's path in 1 out of every 14 shots or so.

But the bullet doesn't occupy its whole path at the same time. A bullet 25mm long occupies 25/91000 = 2.7e-4 of the total 100-yard path length. So the probability of the bullet and the raindrop being in the same place at the same time is 0.07*2.7e-4 = 1.9e-5, or 1 in 54,000. Ergo, there is no need to worry about a bullet encountering a raindrop under these conditions.

a poster on accurate shooter forums did the same calc as was done on the previous page, but added the time of flight of the bullet. odds are 1 in 54,000.

 

[Llama Bob]

So the bullet pushes the air which pushes the rain drop. The rain drop has mass and momentum and will try to resist a change in velocity i.e. acceleration. I think Newton mentioned something about equal and opposite in his third law.

This is a solid argument. If the bullet pushes the rain, the rain pushes the bullet. Can't be any other way.

I think a more likely explanation for why nothing happens typically is that even when it's raining heavily, the air is mostly just that - air. The chances of hitting a water drop, even in heavy rain, are low.

 

[Gtscotty]

That is not a glob of liquid, it's a lead projectile fired from another gun intersecting with the pistol bullet.

I always figured they were probably lead shot, given their bullet-esque velocity, and the practical difficulties that would attend hitting a bullet with another single projectile.

 

[General Geoff]

http://forum.accurateshooter.com/threads/effect-of-rain-on-accuracy-at-100-yards.3864243/page-2

a poster on accurate shooter forums did the same calc as was done on the previous page, but added the time of flight of the bullet. odds are 1 in 54,000.

I love it when math provides a solution!

Though if you push the target back to, say, 300 yards, and have a legit deluge instead of a light rain, those odds probably increase by quite a bit.

 

[JohnKSa]

Here's an accurate answer, but with no solid answers for the really hard questions.

Will rain have an effect on a bullet? Yes. If the bullet interacts with/hits a raindrop there will definitely be some effect on both the bullet and the raindrop.

Hard question: How much of an effect? Offhand's answer provides some insight--an easily noticeable effect.

Is it likely that a bullet will interact with/hit a raindrop? Unlikely.

Hard question: How unlikely? It depends. The heavier the rain, the larger the bullet and the longer the range(longer the time of flight), the more chance that the bullet and a raindrop will try to occupy the same space at the same time.

 

[JohnKSa]

How much of an effect?

I've been thinking about this and came up with a couple of variables that would likely change the amount of the effect.

The distance between where the bullet and the raindrop have their interaction and the target is a significant variable. The farther away from the target the bullet is when the raindrop perturbs it, the more it will have travelled off course by the time it hits the target.

The way the bullet hits the raindrop is a significant variable. If the bullet centerpunches the raindrop, that would probably have less of an effect in terms of deflection than if the raindrop hits one side of the ogive.

So centerpunching a raindrop a few yards in front of the target might have almost no effect on the point of impact. But a glancing hit a few yards from the muzzle should cause a lot more deflection on the target.

 

[Skylerbone]

Then you'd better figure muzzleblast for your load and note that that distance will be snow free as hot gasses blast it away to vapor. Next figure muzzle velocity being higher than any other point in flight as another factor.