Let this be known: I have NOT tried this nor do I intend to unless this has been established as a safe practice.

I was cleaning a rifle last night with compressed air when I tilted it at too far of an angle. The propellant sprayed out onto the barrel, naturally cooling it immediately. That's when I had this question/idea:
While at the range, firing several rounds, the barrel naturally heats up. For anyone that babies their rifles, letting it cool down between groups to prolong barrel life can take a decent amount of time. Has anyone tried accelerating the cooling of the barrel using the propellant in compressed air? My instinct says it could shock-cool the metal, potentially damaging it structurally. However, I thought I'd ask anyways.

Thanks and regards.

No, such thoughts have never entered my head and I am wondering why they are in yours.  Know a good Phd?

One of those compressed air cans?  No fucking way.

A simple fan of ambient air to simulate wind?  Probably OK.

If you "baby" the thing, don't cause vast differences in the temperature of the parts, especially not quickly, if you don't want a warped or strength-compromised barrel.

Doesn't the thing spray super cold air when turned upside down?  Like freezing temps?

its also can make u high and i believe it is flammable.

i do use it however to clean out dust and debris from inside the lower here in iraq. and my computer. so i can keep shooting and arfcomming. maybe not so much the shooting.

I have seen a guy use one of those battery powdered air pumps like you use to blow up an air mattress. He would blow air through the bore and it seemed to work pretty well.

its not air.

Canned 'Air' is not air... It's a compressed liquid that turns to a gas when released...



Which is why if you spray it 'upside down' you get the sub-freezing temps and frost-effect - the liquid sprays out and then vaporizes....



And no, rapidly cooling hot metal is NOT a good idea... Very bad for the metal....

I was in the process of typing a detailed response regarding the thermodynamics, heat transfer, and materials science processes at work with what you are proposing, but aborted due to the late hour.

The gist of it is that it is highly unlikely that you will cause microstructure changes to the material itself unless the barrel is glowing red hot, but you will almost certainly induce dimensional changes due to the localized accelerated temperature change.  This is fundamentally a bad idea.

Correct, and correct.  The cans are filled with refrigerants (hydrofluorocarbon, hydrochlorofluorocarbons).  Tossing these onto a hot barrel in open air where they evaporate immediately is a fantastic way to cause metallurgical failure in your barrel.

In a pressurized sleeve would be another story somewhat, but for these purposes - NO.

By baby, do you mean stick to the sustained rate of fire?

But since a barrel heats unevely does cooling unevely really matter?

The barrel heats unevenly, but by and large the barrel, across it's entire length is generally the same temperature for the sake of this discussion.  Murderman is correct that it's a poor idea as rapidly cooling any metal is not a sound idea, particularly in the case mentioned by the OP as cooling will be relatively localized, RAPID, and uneven.

I can't find it... but there was a vendor that designed a magazine body with a small high volume battery operated fan built in.

The concept was to cool AR barrels after full auto.  Lock bolt back, insert fan-mag, it blows cool air down the barrel.  I looked and ran out of desire before I ran out of was to search.

It's out there... maybe some one has more patience or time than me!

Marc Norlin of Norlin Enterprises developed a cooling system using a gas to cool the barrel. The project originated from his benchrest and prairie dog shooting. I forget what gas he finally settled on using  but it took a lot of experimenting to get the right combo of gas volume and type of gas. He also made chamber adaptors and sold a neat stick-on temp gage to put on a barrel. I haven't seen him for a couple years so I don't know if he's still active with his business or not. It was a very effective system.

I have heard of hard core varminters cycling antifreeze through their barrels through the bore guide.
It's supposed to work pretty well, and it's not as drastic as the canned air.

DevL, you are correct that the barrel does indeed heat up unevenly, but assuming that it is symetric in cross section at each point along its length, the disparity would be in the longitudonal direction rather than radial.  As the thermal conductivity of carbon steels is quick good, thermal equilibrium is pretty rapidly achieved along the length.  As we all know, one can heat up a barrel very rapidly.

Considering that the thermal expansion coefficient for carbon steels is on the order of 10^-5 in/in/F, one could expect a 16" barrel to theoretically grow in length 0.160" at 1000F.  The corresponding radial growth would be 0.002" for a 0.750" diameter barrel with a .224 bore.

The problem with what the OP is proposing is that the propellent used in "canned air" is a gas at atmospheric pressure, but a liquid when pressurized.  When the liquid is released, it experiences a phase change extremely rapidly, and the associated heat of vaporization is substantial.  The expected irregularity of application would tend to be in the radial plane, with corresponding localized "bending" of the barrel so induced.

You have watched me pour bottled water on our cans to cool them down more quickly.  The difference is that fluid is a liquid at atmospheric pressure, and vaporization is much slower and correspondingly evenly distributed as the water covers the entire surface of the devices.  

As a practical experiment, pour some ambient temperature water on your hand....no wahalla.  Then spray some "canned air" on your flesh, and it will get "frostbite" when the water in the cells immediately freezes.