Re: Do black barrels cool faster?
Strange topic for my first post but here goes.
There are three ways energy can move in "heat" form, conduction, convection, and radiation.
When looking at the cooling of firearms as a single body we can pretty much eliminate the conduction piece of the puzzle.
Convection is the direct transfer of heat to the air which then will form air currents bringing more cool air into contact with the barrel, this is where fluting etc will come into play.
Radiation is the energy radiated in the electromagnetic spectrum, everything that has mass is constantly emitting and absorbing this form of energy. Emissivity is a characteristic of a surface which relates to how well that surface will emit, absorb, and reflect energy. The maximum possible emissivity is 1 which as has been previously stated is known as a black body, a perfect emitter and absorber of thermal radiation where none of the energy is reflect off the surface.
Anyways long story short, color really has nothing to do with it. Bare metals have extremely low emissivities and are therefor extremely inefficient at radiating heat energy. This is why coffee pots etc have polished stainless finishes and why many insulated mugs have a back to back stainless finishes separated by a vacuum. A polished stainless steel rifle barrel is going to be the exact same, unable to release its heat in the form of radiation. A bead or oxide blasted barrel is going to be marginally better, but still low on the overall scale.
Surface condition is always going to play a bigger part in emissivity than color, anything shiny, smooth or glossy is going to have a lower emissivity and therefor not radiate heat as well.
Good news for gun owners is that pretty much every coating out there with a matte finish is going to have an emissivity above .9 (same goes for matte interior house paints including white). Blued finishes are going to be dependent on whether it was polished or blasted etc. I've personally verified parked metal, ionbonded metal, and a couple ceramic coatings with an infrared camera to verify they are .9 or higher. Its hard to accurately measure stainless steel barrels because of how reflective they are. As stated above, avoid anything glossy because for the most part if it reflects visible light it also reflects thermal radiation. (thermal reflectivity and emissivity are inversely proportional)
Now, the part of color that does matter, which was hinted at above, is that black stuff gets hot in the sun. The majority of our suns energy is emitted in the visible spectrum not in the infrared, so black surfaces will absorb that energy much better than lighter colored surfaces. So if your concerned with the solar heating of your firearms finding a lighter shade finish that still has a very high emissivity will yield the coolest barrel.
Fun fact is that your barrel is going to cool substantially faster on a clear day compared to an overcast day. This is because on a clear day your barrel is literally radiating its energy into space, and space is COLD so its not emitting much back into your barrel, the atmosphere does provide a small insulating effect but its very minimal. When its overcast you now have a substantial layer of thermal radiation insulation between your barrel and space.
This has always been an interesting topic for me as I have never understood the use of bare stainless steel rifle barrels in any situation where heat buildup is a concern. I am still hoping to do a direct semi-scientific comparison one of these days when I get some spare time and get a manufacturer to donate me some chopped-off pieces of stainless barrel blanks.
For anyone more interested just google "emissivity of materials" and look for some lists. You'll notice that far and away most materials in our world are high emissivity and that bare metals comprise the vast majority of low emissivity materials.