rapid cooling hot barrels

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shekarchi

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Just wanted to share this with anyone as inpatient as me who wants to get the most out of his/her range time... I had started a thread about what would happen if you used an ice pack to cool your barrel so you could get back to shooting instead of waiting around... I wrote a materials engineering professor at U of KY. This guy knows his stuff...
Here is what he said.
Have a great weekend!
Gentlemen I heard back from Associate professor of materials Science. I guess whoever said there is a chance of warping the barrel is probably right...

Here is his reply to my question about using ice-packs to cool a hot barrel...
Have a great weekend all

Interesting question … I looked into this a bit and it seems that most barrel steel is 4140 steel, heat treated to relieve stress at 600 C and then slow cooled. So if you were to heat the barrel by rapid firing, it should not be a problem (I am not sure, but I doubt that firing would raise the temperature to 600 C) since the elevated temperature should not affect the steel microstructure and hence mechanical properties such as hardness would remain the same.

However, the method of cooling could possibly induce stresses and/or warpage in the barrel, which you of course want to avoid. Standard heat treatment would be followed by slow (air) cooling, with no stress buildup. If you were to accelerate the cooling in a uniform way, you could also avoid inducing stresses in the barrel. However, if you were to cool one part of the barrel quickly, with the rest of the barrel cooling afterward (and more slowly; also with some heat transferring back to the already cooled region), then yes, I think you could warp the barrel. Perhaps not enough to see, but this might have an influence on shooting accuracy.

If you do want to try your rapid cooling idea, you probably want to test this method on a barrel you would not mind warping. Basically, I think there is a real possibility you could affect your barrel's accuracy.
 
However, the method of cooling could possibly induce stresses and/or warpage in the barrel, which you of course want to avoid. Standard heat treatment would be followed by slow (air) cooling, with no stress buildup. If you were to accelerate the cooling in a uniform way, you could also avoid inducing stresses in the barrel. However, if you were to cool one part of the barrel quickly, with the rest of the barrel cooling afterward (and more slowly; also with some heat transferring back to the already cooled region), then yes, I think you could warp the barrel. Perhaps not enough to see, but this might have an influence on shooting accuracy.
Click to expand...

I don't disagree with this in terms of theorical warping. I have shot miliary ammunition in old bolt guns till the things were unpleasant to hold. Then I poured water down the chamber and the water boiled and blew out. Then I poured more until it ran out of the muzzle. Messy but worked.

But, given that these are crappy barrels and that I would never shoot rapid fire with a match barrel till it got that hot, because of throat erosion, so what if it warps? You rapid fire a barrel till its real hot, it won't be long till its a tomato stake.
 
I take several rifles on each trip. One gets hot, it goes in the rack with the action open to cool. Then another one gets to play.
 
Safest way to cool is forced air. A half inch hose on a small compressor with a ball valve cut off works well. On a bolt rifle, remove bolt, put in back and turn on air to just get the cool air moving through the barrel. Might take a big rubber band to hold in place if rifle placed vertical while cooling.

Generally speaking if you don't fire over one round per minute you can shoot it long periods as it will not get that hot.
 
I use a 12 volt air mattress pump to cool my barrel ... I usually load all my shooting stuff into the bed of my JD Gator and drive out to the range ... it has a 12 volt jack to plug the air pump into...
 
Most of this is kind of common sense.

Now, here's an interesting twist-
Let's say you drape a wet rag over the top of the barrel, so that the top and sides are covered, but the underneath is not covered by the wet rag, as it would be draped past it but not against it.
Then you start shooting. Would the barrel warp, from the bottom getting hotter than the top (and therefore expanding at a different rate than the top), or do you think the rag would get hot and evaporate all the water before it would become an issue? I suppose part of it would have to do with rate of fire also...
 
Yes.

Anytime you apply an ice pack or wet rag to a hot barrel on the top only?

It is going to cool one side faster then the other, and warp the barrel off where it was before you do it.

So, don't do it!!

It's a genuinely bad idea!

A cooling air stream or cooling liquid through the bore, or letting it take it's own sweet time to cool off on it's own, is the only way possible to cool a barrel evenly on all sides at the same time and preventing it from warping out of shape as it cools.

rc
 
Consider this, for those who doubt what the differential cooling rates can do:

Submarines, when they return to port and shut down the engine room, place themain engines "on the jacking gear" for a period of time as those pieces of steam driven components cooled down to ambient.

The purpose is to slowly rotate the shafts of these items continuously as they cool to ambient to avoid shaft warping which would take place when one side cools down faster than another. And yes...this makes a difference. A warped shaft causes horrible vibrations and may cause severe damage to turbine blading.

A rifle is SUPPOSED to be a precision instrument in its own right, often capable of some pretty insane accuracies. We see what happens to accuracy based on ammunition type, manufacturing tolerances, rifle construction, barrel fouling, and yes...operating temperatures.

So it should come as no surpise that differential rapid cooling of a barrel MAY adversely affect accuracy. Perhaps only temporarily, perhaps permanently.
 
forced air.

there's a reason some (most?) machine guns fire from an open bolt.
 
Lots of benchresters use water-down-the-barrel to cool the barrel. They'd have discovered warp by now, if it were happening. ;)
 
How hot is "hot?"

How much warpage is "warped?

How much initial warpage is results in permanent warpage?

Are all barrels the same?

My point is, you can expect varying results depending on physical variables, and depending on your expectations.

I would expect an ice-towel on one side of a red-hot buggy-whip barrel to have a different effect than a controlled flow of water on a warm-ish bull barrel.

I've done some ammo testing with a standard "HBAR" profile AR-15, where it was necessary to cool the barrel between chronograph strings. I used an inverted can of "keyboard duster" to blow the liquid from the can down the bore of the barrel. The barrel was by no means "red hot," but it was hot enough that it would burn your hand if you grabbed it. Didn't seem to hurt anything that I could discern.
 
I never saw a fellow Benchrester use water to cool a barrel, or even heard of it being discussed. Maybe things have changed, but I never saw anyone doing anything to cool a barrel.
 
A helmet or two of rice paddy water poured on the barrel and receiver of an M-60 gives you an extra hundred rounds after the barrel glows red. sometime the gas plug warps and binds up.

ditto for mortar tube but there's no gas plug to warp.
 
I've never had a decent made barrel correctly fit to the receiver change point of impact shooting rounds every 20 to 30 seconds for 25 to 30 shots going from ambient temperature to way too hot to touch. And match rifles shooting 10-shot rapid fire matches putting a round downrange every 5 seconds will easily shoot sub 1/2 MOA at 300 yards doing this event twice in 5 minutes. Even watched match grade 7.62 Garands tested in accuracy cradles shooting 3 clips of match ammo in 2 minutes put all 24 rounds inside 3 inches at 300 yards. One guy shot his machine rested .308 Win 40 times and put all the bullets inside 2 inches at 600 yards shooting once every 20 seconds.

Such rates of fire does not heat the barrel enough to change its rigidity; they still whip and wiggle at the same frequency for every shot.

Most factory sporters' barrels are fit to receivers whose face is not squared up with the barrel chamber axis. The high point puts an extra stress line at that point as the receiver and barrel metals expand from heat. Therein lies the cause of shot stringing when the barrel heats up.

Another cause I've observed is a bedding pad under the chamber area in bolt guns. The barrel expands from heat increasing the pressure on it at that point and elevation shot stringing happens.
 
I live in the high desert country of Nevada. Ambient temps in the summer frequently reach 100 degrees or more, which means that it takes very little shooting to heat a barrel, and cooling takes forever.

I have a dedicated shooting van, and in summertime I take along a one-gallon jug of ice water and an "air pig".... a tank of compressed air of about ten gallons' size. It is filled to around 120 psi. The water jug goes on top of the van, and gravity-feeds to the benchrest (inside the vehicle) through a plastic tube.

I also have a digital thermometer with a 6" probe, which slips right into the muzzles of rifles of .25 or larger diameter. This is mostly for curiosity, however.

"Hot", to my touch, has proven to be 180 degrees or so. When a barrel reaches that point, I run ice water through the bore for fifteen seconds by count. After that, the bore is dried with a blast of air from the air tank under the bench.

Not only is the barrel cool and dry, but it doesn't change point-of-impact, nor does the "conditioned" state of the bore change..... cast bullet shooters like myself try to NOT disturb the lubricant/fouling state that exists when the barrel has been shooting cast bullets.

I have seen NO negative effects on my rifles from following this routine. In the world of steel, 180-200 degrees is just about meaningless. I don't believe I'm imposing any undue stress on my barrels.... and I DO save a whole lot of valuable range time.
 
Bruce, by flushing the water down the bore (via a modified casing?) you're cooling from the center out so the temporary stresses are balanced all around. If one is going to use water cooling then that is certainly the best way. Also, as you say, you're engaging the water cooling early before the barrel is hot by metallurgy standards. So again you're taking care of business in a way that will avoid creating excess stress in the metal.

By the way, for anyone that is wondering more about this the effect of thin metal being warped by heat is easy to see if you're someone that has welded anything. Run a long bead on a flat bar of cold metal and the cooling of the bead will cause the flat bar to curl like a potato chip towards the bead. The stress that is doing this is the tension in the weld bead pulling along the face of the flat bar. If it was you trying to pull a string or wire that hard to cause the bar to bend can you imagine the tension you'd need?.

In the case of the weld the stress is locked in by having used molten metal in the bead. But in the case of a rifle barrel the stress is USUALLY temporary since nothing gets melted (hopefully :D) Where this can all go south though is if the barrel is SO hot and cooled SO quickly that this temporary side way stress of cooling on one side actually causes the metal to go past the point of elastic deformation and into the plastic stage. If that occurs then the metal stays warped.

"Elastic" in this case being that the metal stays within it's springing range of force. That being the amount of stress which still allows the metal to return to it's original size and shape. "Plastic" is when you bend or stress things past that spring zone and into the range where the bend is permanent.

Frankly the best way to do this would be to air cool the bore. A cooler full of ice with a computer fan blowing air into the cooler and a hose off the cooler to a modified casing will blow chilled air down the bore. It'll take a little longer to cool the bore and metal but the risk of a serious stress rise due to differential cooling is avoided. And best of all you don't need to blow out any water if you only cool it down to where it's ambient or a hair warmer instead of taking it all the way down to cooler than ambient.

Even easier would be a little battery fan into a collector box and a hose to a modified casing. No ice means no risk of condensation. It would take a little longer to cool the bore but with no further effort needed to dry anything it may all work out the same.
 
For the ice-water treatment, I place the jug on the roof of the van and bring a small-diameter plastic tube from it down to the benchrest inside.

With the rifle's muzzle angled downward over the forward edge of the rest, (and OUTSIDE the vehicle!) a valve on the tubing allows me to regulate the flow. I don't need any sort of chamber adapter. The blast of air following the water treatment dries things rather nicely.

Thanks for your comments; they reflect my thinking on this cooling method very closely.
 
thanks everyone for chiming in
all your comments are informative and helpfull to this novice reloader... keep them coming
 
There was a fad a few years ago for integrally cooled barrels.
One was water jacketed and came with a little circulating pump and reservoir.
There was another that blew Freon either down the bore or through a jacket, I forget which.
 
We have a guy that shoots Hi-Power Service Rifle with us that has a AR-15 he bought up in Alaska from NA's that used it for seal hunting, and cooled the rifle off between long strings of fire by dunking it in the ocean.

He does not shoot High Master or anything, but his scores are respectable using the "cryo-rifle"
 
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