polishing a barrel?

If the barrel is being heated from within and not from the sun, black will dissipate the heat more quickly than white.

A controlled test would have to stop firing when a specific high temperature is reached and then timed until a specific low temperature is reached... what these figures would be I have no idea.
 
Black is a better absorber of light, therefore it's a better radiator of heat.
 
Well, this "black bbl. vs. polished bbl." had me do some research. Yes, it is true that a black body absorbs heat energy, and a pure white body reflects it......but this is true only in the visable light spectrum. The sun emits electomagnetic energy which consists of 49% infra-red energy, 50% visable light energy, and 1% untraviolet light energy. In the infra-red wavelength region, all colors including black and white emit and absorb that heat energy well. To sum up one scientist who answered the question "what color should a radiator be?......You will get the same output in BTU's from a white colored stove as one that is painted black. The only caveat is that they should not be painted with a paint that has metallic chips in them as they inhibit heat transfer. The bullet's friction passing through the barrel heats it from the bore ID and this heat migrates to the OD via conduction. I believe the layer of black paint would only inhibit the heat transfer as most paints are a poor conductor of heat. However, the actual numbers are so small that for competitive BR this really does not make a difference in the real world.
 
As in most things, the issue remains, what are you looking for, in the transfer of heat. Heat is transfered by, Convection, Conduction, and Radiation,,,only Radiation is color Dependant. Are you trying to heat a room or shed heat from an object? Trying to heat a swimming pool, or cool an internal combustion engine. Even the color of your roof, or the color of your car are affected.

A polished object will have less surface area than a rough object, thus the transfer of heat will be slower, or less. The amount of heat transfered by radiation depends on the temperature of the object, the emissivity of the surface , and the amount of surface area it has.

People tend to judge heat by touch, and around 140 deg will burn skin, would that even be an issue? How about 200 deg? I've heard people say their vehicle engine is running too hot, because it felt excessively hot when they opened the hood. It better be hot or the proper transfer of heat would not be taking place.

I doubt that barrel color would have little effect, due to the conditions in which it is used, and the short duration.

A hot barrel is transferring heat, whether that's good or bad.

FWIW, The optimum emissivity coefficient would be , E=1.00
Black paint is approx, E=.9
Polished stainless is approx, E=.075
 
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My head hurts!

So you paint a barrel black, and it throws off more heat THROUGH the black paint (The paint in no way acts as an insulator or contains the heat?) Or does the black paint draw more heat into the atmosphere by some mysterious method? I'm not arguing, but I'm sending this to Myth Busters................. :)
 
Nobody's head hurts worse than mine after the last two days of reading scores of physics wizards trying to answer a simple question.....but Dennis apparently is correct a flat black surface will give up heat faster than a highly polished silver surface (discounting any radiation heating from the sun). I can't quite grasp this phenomena, but that's the concensus of the experts. This is what I get for being a skeptic.
 
Dennis Sorensen said:
If the barrel is being heated from within and not from the sun, black will dissipate the heat more quickly than white.
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I think You've mentioned this a few times both here and elsewhere. May I ask what reasoning is behind that finding? From a purely thermal radiation standpoint, I cannot think of any scientific reason why this would be the case. Light is a form of radiated energy as is heat. Perhaps I'm unaware of some correlation between the two in the context we're talking here. And maybe you are right but the quantities are so small as to be insignificant, I don't know. I can think of a lot of things on a barrel that might alter its coefficient of thermal transfer, but, color would not have been one of them. Of course, polishing would not be high on my list either.
 
Dennis Sorensen said:
(A Black Body Emitter (BBE) heat radiating coating applied to the outside of the cylinder and head, will help dissipate any heat that does get through the TBC and is particularly effective on hot-running fan cooled engines.) : http://www.swaintech.com/store.asp?pid=10314.
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Dennis,

I just read back through the thread a bit. Now I see.

I think here is the confusion. The heads you mentioned in that post were more likely to radiate heat because they were painted. Not because they were painted black.

The "Black Body" you mention above is a scientific term for a type of radiant substance, and has nothing to do with color (visible color/radiated light). Well, not in the spectrum of heat anyhow. Paint may well have a higher coefficient of thermal emissivity than polished metals, but that's not relevant to its color unless it is being heated with visible light. At that point, then the visible light does ADD to the heat absorption, but still, does not affect its emissivity.
 
TRA said:
A polished object will have less surface area than a rough object, thus the transfer of heat will be slower, or less.
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When he first produced barrels, Neville Madden capitalised on this, finishing his barrels by cutting a v-e-r-y fine thread on them, probably doubling the effective surface area.

Tunred out that the world wasn't ready for that idea.
 
Geez John,

I had an interesting thought when I read that. According to the original light gun rules of the PA Benchrest, that barrel would have been illegal because of the straight taper rule. Same currently goes for point blank BR here in either of the pbbr rulesets for HV or LV, (unless I'm mistaken).
 
If you have a Dan Dowling smithed Barrel you'll notice it's unique finish. More surface area is like having radiator fins.

Paul
 
Dennis Sorensen said:
Interesting reading > http://www.swaintech.com/store.asp?pid=10314
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If you read that article, you'll see that the top piston coating they use is white.

LHSmith said:
Nobody's head hurts worse than mine after the last two days of reading scores of physics wizards trying to answer a simple question.....but Dennis apparently is correct a flat black surface will give up heat faster than a highly polished silver surface (discounting any radiation heating from the sun). I can't quite grasp this phenomena, but that's the concensus of the experts. This is what I get for being a skeptic.
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Heat energy is radiated in the far infrared spectrum. It is not visible. The only times we "see" heat is when we see the effect of the heat on some other item, sorta like watching mirage.

At infrared wavelengths, a highly polished metal item becomes a "black body" material. It essentially becomes an insulator. This is why they foil face insulation. It ain't to make it pretty. It radiates less infrared energy (heat). It also accepts less. HOWEVER, put light energy to it (say, sunlight on chrome) and all of the sudden it accepts that heat energy. The visible color of that material has absolutely nothing to do with the emissivity unless the item is heated to where it begins to give off light. When it is red hot, or hotter, now the color will matter because it is now giving off energy in that spectrum as radiant energy.

The idea of reducing surface area by polishing has nothing to do with why the polished barrel is a better insulator. It has to do with the items coefficient of thermal transfer for infrared energy. The polished metal surface is just less likely to transfer (in or out) heat energy.

After all that, who is to say either way is good or bad for accuracy?
 
4Mesh said:
If you read that article, you'll see that the top piston coating they use is white.
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Yes white reflects the heat helping the piston to remain cooler... black heads on snowmobile engines reduced temperatures 40 years ago.

I suspect the temperatures of operating engines is so much above sustained barrel temperatures that what works for engines won't be as effective for barrels.
 
Dennis Sorensen said:
Yes white reflects the heat helping the piston to remain cooler... black heads on snowmobile engines reduced temperatures 40 years ago.
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These two situations are entirely different. The white ceramic coated piston is reflecting heat so as to not absorb it in the first place. The white ceramic coated piston is exposed to extremes of visible light (flame inside the cylinder) for 1/4 or 1/2 of it's operating time, (2 or 4 stroke). That is not the case with the exterior of the heads. The reasons for these two situations are not even closely related to each other, and while the paint idea can apply to gun barrels, it is not for the reasons suggested by a few folks in this thread.

Folks should differentiate between heat radiation, and heat absorption. The SUN makes heat and transmits it in the form of visible light energy (and plenty as ir as well). Visible color of an item will absolutely affect how well it will absorb that heat energy because it is in the visible spectrum. Its color will NOT affect how well it will give that heat back off as radiated heat. Again, till it's red hot. Its color will also not affect how well it will absorb the IR energy from the sun.

So, you could think of it like this. If you have a 300 Degree F item in a room, will it cease to cool off because you turn the lights off? Other than the heat energy it picks up from that light, will the light have any effect whatsoever on the item? No.

Now, with the lights off, paint the item 5 different colors with otherwise identical paint. Will that make any difference in how fast the item cools. No. The only difference it will make is if the paint is a better or worse conductor of IR heat. If the paint is a better conductor, it will cool faster. If the paint is worse, it will cool slower.

I suspect the temperatures of operating engines is so much above sustained barrel temperatures that what works for engines won't be as effective for barrels.
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As I said above, till the item is so hot it begins to give off light, it's color is irrelevant.

Another great way to think of this is to think about sunblock. SPF90 or whatever. This stuff does not insulate from heat to any measure, if it's hot outside, you get hot. It doesn't block light to any degree, your skin is still highly visible, just as much so as it was before you put the sunblock on. But, it does block Ultraviolet, a form of energy you cannot see. Again, no effect on the visible light spectrum, much effect on the UV spectrum.

Plexiglas is a great example of a substance that is virtually opaque to IR, yet transparent to visible light. Two different energies.
 
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Old Chinese proverb.....Although some may appear to have expertise in these matters, their facts are in error.
 
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Given that testing is so doable, I think that that is the way to go. The problem with the application of theory is that it can be misapplied, which is why they are tested. One of the first posters shared some of his field test data. I tend to go with that.
 
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