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Thread: BUIS in humid climates and A/C

  1. #1
    Site Supporter OlongJohnson's Avatar
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    BUIS in humid climates and A/C

    Thinking about optics and what can go wrong, in the context of making decisions about BUIS.

    I realized that I have often had a problem with the simplest of optics: sunglasses. Here in SE TX, on a lot of days, if I put on sunglasses in the air conditioned office, or have them on in the car, and step outside, they immediately fog up for at least 20-30 seconds. It seems that this is a likely, perhaps the most likely failure mode I can expect to encounter in use of a defensive optic-equipped arm in this environment. And due to the greater thickness (thermal mass) and the fact that air is only circulating on one side of the lens, a firearm optic (scope or closed-emitter dot) is likely to take longer to unfog.

    Fogged glass on two ends of the optic will render a cowitnessed front sight useless, regardless of the rear sight. So it seems that if this swamp-arse humidity fogging is the concern, the lower-1/3 vs absolute cowitness argument is missing the point. If one is stepping outside and needing to shoot something, one more than likely really needs at least the ability to shoot that thing NOW. And the only solution to bridge between stepping into the humidity and the lenses warming up and unfogging themselves is offset sights (or just dedicate the gun to irons).

    I haven't actually experienced this fogging with a rifle optic yet, but I know there are a lot of carbine users around here and throughout the Swampy South. Am I larping my way into a non-situation? Or is this actually a thing that pro users deal with? I'm reckoning more than one person here has had a carbine in a vehicle with A/C and stepped out into the humidity needing to use it right away. Would like to hear some input from the voice of experience.

    @Rex G @SouthNarc @Wayne Dobbs @HCM @Chuck Whitlock @LSP552 @HCountyGuy
    Last edited by OlongJohnson; 11-20-2020 at 10:21 AM.
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  2. #2
    Site Supporter Totem Polar's Avatar
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    Tag @GJM on this one, too.

  3. #3
    Site Supporter OlongJohnson's Avatar
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    Forgot @John Hearne
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  4. #4
    Ben Stoeger advocates practicing with the lens taped over so you use true target focus. Fog or other debris on the lens is certainly no worse than black tape.
    Likes pretty much everything in every caliber.

  5. #5
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    Quote Originally Posted by GJM View Post
    Ben Stoeger advocates practicing with the lens taped over so you use true target focus. Fog or other debris on the lens is certainly no worse than black tape.
    Is he putting it on the front and back of the optic to create an opaque blob, or just the objective to obscure the target but not the dot?
    im strong, i can run faster than train

  6. #6
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    A month ago I was calling coyotes and breathed on my scopes ocular lense. Conditions must have been just right cause it fogged over completely. I pondered about what would’ve happened in a life or death situation and even though I have QD scope mounts and flip up irons, they are not an immediate action solution. My thoughts then were for off set irons or a red dot.

    Following...

  7. #7
    I have also been thinking about this since after a three gun stage when I was trying to hit a 200yd plate in the pouring rain. I was trying to look at the plate and then move my EOtech to where I think the plate was.

    ETA: Managed to hit 1/6, but not sure how many I would have hit without the rain...

  8. #8
    Iron sights on an AR in rain you’ve got to blow the water out of the rear peep after every shot.
    I'll wager you a PF dollar™ 😎
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  9. #9
    Quote Originally Posted by UNK View Post
    Iron sights on an AR in rain you’ve got to blow the water out of the rear peep after every shot.
    But you can. My optic was like a car with no wipers that wasn't going fast enough for the wind to push the rain anywhere.

  10. #10
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    I'm not really the guy to help you. I'm not currently running any optic, mostly due to analysis paralysis and funding, so I run with a same-plane rear aperture and tritium front from XS. I don't recall having any issues when running an EO Tech, but that was up in the midwest, and I don't really remember any instances where I deployed the rifle.

    For what it's worth, it doesn't get much more hot and humid than in the Corpus area. The only fogging issue that I've had with sunglasses has been from exiting buildings, not my vehicle. I keep my vehicle A/C at just "comfortable" level, not "stiff nipples" level.


    Quote Originally Posted by UNK View Post
    Iron sights on an AR in rain you’ve got to blow the water out of the rear peep after every shot.
    For this reason and others, I like the idea of combining a LPVO with one of XS's offset express set ups, although the front sight isn't real protected...maybe something like a hooded HK-style front. In the "Oh, shit!" scenarios we are envisioning, I feel the express rear would be faster and accurate enough versus an aperture. (I leave the large aperture up by default)

    https://www.xssights.com/Products.aspx?CAT=8279
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