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Thread: Does spray paint delay barrel cooldown?

  1. #11
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    Quote Originally Posted by Clint View Post
    What kind of base barrel finish are you having rust problems with?
    Good question. The only time I've found a little rust was on an after markets upper where the barrel wasn't phosphated under the FSB. Even then, it was on a gun that definitely got wet and banged around in the desert, and the rust was minor/surface stuff that wasn't causing any issues.
    "You people have too much time on your hands." - scottryan

  2. #12
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    Quote Originally Posted by crosseyedshooter View Post
    Something to keep in mind, any coating designed for "shedding heat" will likely have higher emissivity than bare metal in the infrared spectrum. It may be more visible to NVGs like reflective paint.
    Interesting point.

  3. #13
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    I test this years ago. not a lab-quality test but...... I took 4" lengths of 1" diameter steel and did them up different ways:
    Fluted and blasted
    No flutes, blasted
    Polished
    Blasted and painted black

    The ends were capped with Transite, a high-temp insulator, since I wanted to test only what was radiating from the "barrel" diameter. I heated it all up to 400 in the oven-- for about an hour to make sure sure everything was up to temp down to the core. The reason for the test, mainly, to see if fluting was really a big deal to cooling and also, like you, I thought paint would be an insulator even though black color is an aid in radiating heat-- why race bikes used to come with black-painted cylinders. Using a hand-held IR pyrometer, I tracked the cool-downs.

    Bad news--I have long since lost the actual results, in the shuffle of things over two decades. BUT. I recall the fluting having almost no discernible positive effect, the paint having no discernible negative effect. Note that the fluting was shallow like most for-show-only factory fluting; and the paint was put on purposely as thin as possible. What made the big dif, as predicted by the Machinery's Handbook: polished surfaces radiate heat poorly, basically that surface "bounces" the heat back in. The rough blasted vs/ polished was the biggest difference,m with the fluted having, as I say, a tiny, tiny advantage.

  4. #14
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    Quote Originally Posted by crosseyedshooter View Post
    Something to keep in mind, any coating designed for "shedding heat" will likely have higher emissivity than bare metal in the infrared spectrum. It may be more visible to NVGs like reflective paint.
    If it helps it cool down faster itíll be visible for a shorter time though.


    Sent from my iPhone using Tapatalk

  5. #15
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    Is it black now? A "black body" will radiate more heat when hot than a body (in this case a barrel) of another color.


    It is an ideal emitter: at every frequency, it emits as much or more thermal radiative energy as any other body at the same temperature.

    https://en.wikipedia.org/wiki/Black_body

  6. #16
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    Quote Originally Posted by Ned Christiansen View Post
    I test this years ago. not a lab-quality test but...... I took 4" lengths of 1" diameter steel and did them up different ways:
    Fluted and blasted
    No flutes, blasted
    Polished
    Blasted and painted black

    The ends were capped with Transite, a high-temp insulator, since I wanted to test only what was radiating from the "barrel" diameter. I heated it all up to 400 in the oven-- for about an hour to make sure sure everything was up to temp down to the core. The reason for the test, mainly, to see if fluting was really a big deal to cooling and also, like you, I thought paint would be an insulator even though black color is an aid in radiating heat-- why race bikes used to come with black-painted cylinders. Using a hand-held IR pyrometer, I tracked the cool-downs.

    Bad news--I have long since lost the actual results, in the shuffle of things over two decades. BUT. I recall the fluting having almost no discernible positive effect, the paint having no discernible negative effect. Note that the fluting was shallow like most for-show-only factory fluting; and the paint was put on purposely as thin as possible. What made the big dif, as predicted by the Machinery's Handbook: polished surfaces radiate heat poorly, basically that surface "bounces" the heat back in. The rough blasted vs/ polished was the biggest difference,m with the fluted having, as I say, a tiny, tiny advantage.
    This is in-line with my experience and data.
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  7. #17
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    I watched a video on Youtube recently of some folks testing air temps on intercoolers (for turbochargers); unpainted aluminum vs black (or flat black). The painted intercooler had cooler output air temps.

    It wasn't scientific testing, but my takeaway was that paint probably isn't going to hurt anything.

  8. #18
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    Quote Originally Posted by Ned Christiansen View Post
    I test this years ago. not a lab-quality test but...... I took 4" lengths of 1" diameter steel and did them up different ways:
    Fluted and blasted
    No flutes, blasted
    Polished
    Blasted and painted black

    The ends were capped with Transite, a high-temp insulator, since I wanted to test only what was radiating from the "barrel" diameter. I heated it all up to 400 in the oven-- for about an hour to make sure sure everything was up to temp down to the core. The reason for the test, mainly, to see if fluting was really a big deal to cooling and also, like you, I thought paint would be an insulator even though black color is an aid in radiating heat-- why race bikes used to come with black-painted cylinders. Using a hand-held IR pyrometer, I tracked the cool-downs.

    Bad news--I have long since lost the actual results, in the shuffle of things over two decades. BUT. I recall the fluting having almost no discernible positive effect, the paint having no discernible negative effect. Note that the fluting was shallow like most for-show-only factory fluting; and the paint was put on purposely as thin as possible. What made the big dif, as predicted by the Machinery's Handbook: polished surfaces radiate heat poorly, basically that surface "bounces" the heat back in. The rough blasted vs/ polished was the biggest difference,m with the fluted having, as I say, a tiny, tiny advantage.
    Most barrel cooling is through convection, not radiation, So what you want is a high contact area and high air flow over the barrel, which is why the Lewis machine gun cooling system worked so well...

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