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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/19/2006 at 14:32
Mike McDonald View Drop Down
Optics Journeyman
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Joined: September/01/2004
Status: Offline
Points: 733

Shooting in a Downpour


Thought this information might interest some of you.


Had another opportunity to shoot in the rain last week, and as my wife reminds me, I'm not made of sugar so I won't melt, which is good enough reason to pursue  my hobby further.


Quite a few folks have never shot it the rain and wonder what it does to bullet flight.  Theoretically all those little droplets hitting the bullet must knock it off balance rendering it impossible to hit what you're aiming at.


Not so.


When we fire that speedy little pointy thing from our modern rifle it's going supersonic and creates a bow wave in front of the bullet.  Essentially the projectile operates in its own atmosphere surrounded by a pocket of air which parts those droplets keeping the bullet on a straight path to the target.  The effect on accuracy is limited for the most part by shooter ability to see the target in the rain.


There are other things happening though………………………..


When a bullet is fired from a rifle, a partial vacuum is created as the bullet and expanding gasses exit the muzzle.  As this vacuum of sorts equalizes, air, and in this case, water, is introduced into the barrel of our rifle.  So far the 1st shot went where it was aimed.


2nd shot.

Now our shooter is back on target ready for shot two.  Things are going to be different this time.  The rifle barrel usually full of a gas called commonly referred to as air now has another element inside.  Water.

Air as we all know is  a compressible substance.  Water does not compress and here in lies a problem.

We can compress the column of air in the barrel ahead of the bullet but that water isn't going to get out of the way.  This obstruction is going to raise pressure in the cartridge case and chamber, possibly to unsafe levels.  When the rifle is fired, pressure rises quickly, but the bullet may not speed up in an equal amount to the pressure increase, due to the extra work it is doing trying to move all that water.  Because of this increase in pressure, and the resultant barrel harmonics it causes, our bullet does not go all that close to where we wanted it do go in the first place.

As an example, at 600 yards, shot two is 8 inches from shot one, with the same point of aim.  That assumes our shooter is pretty good on a normal day.

With the current trend toward long range hunting that 8 inches is a wounded animal that has to be shot again.  In the rain it's not good to assume that subsequent shots would be all that accurate not from the rain interfering with bullet flight but from the ancillary things caused by the water vapor.  Result is an escaped animal or one that has to be tracked, and shot yet again.  Anyone care for some hamburger?

Another factor is we're shooting in a rain, so when the shooter cycles the action, the cartridge to be loaded gets wet.  This is not good  A fired case expands rapidly and grips the chamber walls, helping to hold it in place until pressure reduces to a safe level. Over simplified somewhat but you get the idea.

Now we've reduced that ability by lubricating the case, causing the cartridge head and the bolt lugs to endure much, much more pressure than normal.  This is a dangerous situation.  In a weak rifle the results could be unpleasant indeed.


[A side note about action strength and testing.

In the U.S. actions are tested, or proofed, by loading a cartridge with powder to generate a substantially higher than normal chamber pressure.  After firing this load, the action must function as normal, and measurements of the action must not exceed a given tolerance.  This pressure is substantially above normal operating parameters.  The British just place a lubed case inside the chamber to get identical results.]



I've enclosed a couple pics of cases fired dry, and again wet, to illustrate what happens to the cases.

dry cases 

wet cases

The rifle that shot these cases needed the bolt locking lugs refinished afterward to be safe.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/19/2006 at 14:36
cheaptrick View Drop Down

Joined: September/27/2004
Location: South Carolina
Status: Online
Points: 20351
Excellent post, Mike. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/19/2006 at 16:32
lucznik View Drop Down
Optics Master
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Joined: November/27/2004
Location: United States
Status: Offline
Points: 1436



That really places new meaning to the old phrase "keep your powder [or in this case barrel/action/ammunition] dry."

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/19/2006 at 16:48
Trinidad View Drop Down
Optics Master
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Joined: May/04/2006
Location: United States
Status: Offline
Points: 1555
Great post Mike.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/20/2006 at 15:37
Anthony View Drop Down
Optics Apprentice
Optics Apprentice

Joined: June/01/2006
Location: United States
Status: Offline
Points: 223

thanks for the info, It's always good to be warned about things like this before I can make the mistake.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/20/2006 at 15:47
Stephanie View Drop Down
Optics Goddess

Joined: February/13/2004
Location: Native Texan
Status: Offline
Points: 1502

Not in the rain, but here are some clips of a bullet in slow motion...




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