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  #1  
Old 02-20-2010, 07:43 AM
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Rain And Its Effect On Bullets


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A frriend that works in a ballistics lab did and experiment on the effects of a rain drop hiting a bullet. The conclusion was that a perfectly stabilize bullet did not lose any accuracy , in other words no effect. A marginaly stabilized bullet is knocked off course by a single rain drop.

Interesting to say the least and IMHO illistrates the supirrioity of plenty of stabilization

Last edited by jwp475; 02-20-2010 at 09:17 PM.
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Old 02-20-2010, 08:21 AM
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That is very interesting. I would also be interested to know what the gyroscopic stability factors were for the bullets in the tests? Too little spin makes a bullet vulnerable to small influences. Too much spin increases wobble from any mass asymmetry and reduces ballistic coefficient by increasing bullet yaw, so you don't want to overdo it. But it would be interesting to know what numbers he was actually working with?

If he doesn't have the numbers figured, perhaps he can provide the weight and length of the bullets used, and the muzzle velocities and the barrel twist rates used so I can figure them out?
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Old 02-20-2010, 08:52 AM
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Hmmmmmm ???

As stated in another thread,given the bullets shock wave,and given the bullets temperture coming outta the bbl,and considering that it could be spinning(rotational velocity)at quarter of a million RPM's+,it would amaze me if the bullet would even come in contact with the water droplet.----pruhdlr
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Old 02-20-2010, 09:02 AM
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He's talking about bullets fired specifically not to be spinning fast enough for good stability compared to those that are. No velocity is given. If the lab did this at subsonic velocities, shock waves wouldn't come into consideration. We need more information.


The ballistician's cheer: Mo data! Mo data! Mo data! Yay!
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Old 02-21-2010, 01:24 PM
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I remember pondering the effect of insects on bullet flight one summer. Mosquitoes were bad that day. How many were hit on the hundred yard trip I have no idea?

Made me feel better thinking I got a few of them with each shot though....because a few of them got me!

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Old 02-21-2010, 01:49 PM
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I shot a goody amount of benchrest matches in the rain, and it didnt affect the size of the groups or the point of aim...case in point: A match that I won...40 mph switching/gusting tailwinds....poured the entire match...grand aggregate for 100, 200, and 300 yards was .3300..........that gun would shoot those same size groups on clear days with no wind.
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Old 02-21-2010, 01:59 PM
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Flat top,

Did you try it with bullets on the edge of being unstable? Most of us avoid that situation like the plague, but apparently jwp75's friend did it on purpose.


Cheezy,

Mosquitos must have been bad if they cut your trip to just 100 yards!

A couple of friends of mine did an overnight hike through the Everglades decades ago. They slept in hammocks with mosquito netting, and reported awakening unable to see out through the netting; just the solid gray of the mosquito layer. Clearly a sport for young men with strong bladders.

Pruhdir got me thinking that I actually have no idea if a bullet shock wave has adequate force to affect a rain drop enough to clear the water out of the way of a bullet, much less whether it might be able to damage mosquito flight surfaces permanently? It would be cool if it could, cause then you could have taken out more than you expect?

The Myth Busters tried shattering glass with bullet shock waves without success, IIRC? That included using a .50 BMG. You could calculate the energy involved pretty easily if you know the distance from the bullet. You'd just look at the bullet velocity loss over the length of the object in question and calculate the difference in kinetic energy in the bullet. That's how much would be put into the shock wave as it passes. Then you work out the percentage of the shock wave the object in question intercepts? Looked at that way, I'm not thinking a near miss on a mosquito is going to do it in. Especially not if the bullet has a good ballistic coefficient.
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Last edited by unclenick; 02-21-2010 at 02:03 PM.
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  #8  
Old 02-21-2010, 04:44 PM
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Unclenick; My whole goal my entire shooting career has been to shoot stable bullets, and tiny groups!
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Old 02-22-2010, 09:46 AM
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Mine has been to combine stable bullets with a stable shooting platform. Offhand, it's always the latter that is harder to achieve. I heard one instructor refer to it as "awful hand" position, which can't be good psychology with the students, but is apropos for most folks.
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Old 02-22-2010, 01:27 PM
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was reading last night on special sniping situations in Plaster's Ultimate Sniper. at the time of writing he was not aware of any quantifyable research on the balistic effects of rain but was aware of anecdotal evidence that rain water in the last couple inches of your bore can cause your bullets to fail to stabalize. Also found micro cracks in the rifling of the test gun presumably caused by the water during firing. He said in SOG they tap their barrells to make sure there is no water in them. I'm not sure how effective that would be. but if it makes you feel better...

I don't think it stands to reason that the shock wave off of a bullet could affect water ahead of the bullet and therefor keep it from being struck by rain drops. The shockwave has to travel the speed of sound and the bullet would be supersonic so the shockwave would always be behind the round. Not a lot it can do from back there to keep the bullet dry. it seems like water hitting the bullet should drive it down faster making it arc steeper but we may be over estimateing the nuber of dropps that hit a bullet in flight. The density of drops in a squall would have to be super high. If they were high enough to hit the bullet many times the visibility would have likely been too low to take a safe shot.

lets say each drop weighs 1/4 of a grn and is traveling at 20 ft per second straight down and at the moment of collision the bullet is traveling parallel to the ground and weighs 168 Grns and is going 2600 fps. seems kind of like lobbing lemons at a b52
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Old 02-22-2010, 11:51 PM
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Helix as was originally posted, then reiterated by Nick.
NOT talking about the effects of drops on normal bullets. A Bullet that is out of gyro is a whole different realm of physics.
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Old 02-23-2010, 04:00 AM
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Rain doesn't have much (if any) effect on my 270 out to 500 yards.
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Old 02-24-2010, 04:01 AM
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At least for my older eyes the effect of rain on the visual aspect of target acquisition outweighs any physical effect of the rain on the bullet.
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Old 02-24-2010, 06:35 PM
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Helix,

Get hold of a copy of Robert McCoy's Modern Exterior Ballistics sometime and look at the shadow graphs. When the bullet is just barely over mach 1, the shock wave is well out in front of it. The physics is curious.

Out of curiosity, I took a look at the venerable 168 grain Sierra match bullet. At 2500 fps it is losing velocity at a rate of 2 fps/yd. If we suppose a rain drop is an eighth of an inch across, then the bullet should lose about 0.007 fps in the time it takes to pass the rain drop. It works out to about 0.013 ft-lbs passing the rain drop. If we further suppose the drop is about half an inch off the centerline of the bullet, the drop will intercept about 1/64 of the cone of the shock wave, being subjected to about 0.002ft-lbs of shock wave energy, or about 0.00028 joules. Looking at some online physics sites, it turns out to take about 6 times that to divide a 1/20 liter drop into two. More if you break it into more parts. So, I don't think the shock wave will break up the drop ahead of the bullet hitting it.
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Old 02-24-2010, 07:44 PM
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The physics says that if a rain drop hit the shock wave hard enough to affect the water drop, the shock wave would have to affect the bullet the same amount. If shock waves were deflecting water drops, the shock waves would have to deflect the bullet the same amount.

Shock waves are not the explanation, but I'm not sure what is.

Solid water certainly does have an effect on bullets. Rain is obviously not solid water, but logic would suggest that its effect will be in proportion to its relative density to solid water. Rain is a looooonnngg way from solid water.

Just a theory. I have no real information to back me up, but I would love it if someone had real scientific data. Myth busters don't count.
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Old 02-25-2010, 12:40 PM
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Unclenick, I'll have to look at that book. Every graphic I've ever seen of a supersonic object shows the shockwave eminating from the object and trailing. I wonder why a bullet is different. My understanding of this was the the shockwave was a soundwave and could only travel as fast as the speed of sound. The Object moving faster than sound logically meant it would be ahead of the boom. perhaps there is somthing I'm missing. as always your input elevates the thread.
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Old 02-25-2010, 01:01 PM
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Ok so did some googleing. Unclenick. you are correct the shockwave forms just in front of the bullet. I guess I pictured it in my head forming at the point where ithe ogive transitions to the parallel walls of the round or at the canelure. in this shot it is hard to see but the accompanying info showed it slightly ahead of the bullet like a bow wave on a ship.



http://www.absoluteastronomy.com/topics/Shock_wave
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Old 02-25-2010, 04:00 PM
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I think Saskshooter has this right. We think that there is a lot of rain in the air when its raining but there is only so much rain that can fall before we can't see.

I've seen somewhere a discussion of the effect of rain on bullets that entailed the total amount of water in the air during a rain. It was surprising how little water is in air at the same time during the heaviest rain storms. Then you have to calculate the small area that the bullet takes up during it's flight. Ergo no collisions.

Just my thoughts.
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Old 02-26-2010, 05:47 PM
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Some of you are "raining on my parade". No trouble! I have shot some mosquitoes and asion lady beetles. I have no trouble with rain.

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