Relative humidity and guns


January 2, 2007, 10:08 PM
I got a new gadget for Xmas, an Oregon Scientific weather station with a remote sensor that you can put outside to gather outside temperature and humidity. I noted that I can buy additional sensors (it will monitor up to 5), and it occurred to me to toss one in the gunsafe.

That, naturally, begged the question...what is a safe range of relative humidity for firearms? I know that low humidity is better for rust prevention, what is the upper safe level? 40%? 30%? Anyone know?

Also, as a side discussion, how good are Oregon Scientific weather stations? Are there better ones out there for consumers?


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January 3, 2007, 06:42 AM

I also wish to know. I run a dehumidifier (gun room in basement) and find it hard to get the humidity below 20%.


January 3, 2007, 07:06 AM
I don't know an answer to your question about the "safe" upper limit. But, a couple of thoughts. Temperature variation is also important. For a given amount of moisture in the air, the relative humidity will vary with the temperature. For example, if the gun safe is in an unheated/conditioned room, and the temperature drops, the relative humidity in the gun safe will rise.

Also, if rusting hasn't been a problem with guns not in the safe, then there shouldn't be a problem inside the safe.

If you are concerned, a simple precaution would be to get some of those rechargeable moisture absorbing canisters for the safe. Monitor them and see how often they "fill up." You can recharge the canisters by baking them in an oven. Should help keep your guns spiffy.


January 3, 2007, 07:14 AM
I read somewhere years ago that rust is likely to 'spontaneously' begin on most common unprotected blued metals when humidity reaches or exceeds the 50% mark. It seems like I must have learned that from a reliable source because I accepted the info immediately, but I really have no idea what that source was. I am sure, also, that the actual composition of some steels is much more resistant to rust than others.

I live where the humidity is almost always above the 50% mark half the year and my guns never rust, but then I do protect those precious pieces of metal with Breakfree. Over forty years of using guns hard and storing them appropriately with zero rust. I do have one rifle, a Sako, I do have problems with. I don't think the factory bluing process was properly 'stopped' at the factory on the barrel. No regular oil or rust preventive seemed work until I read about and tried ordinary paste wax. Problem solved.

January 3, 2007, 09:05 AM
I've had a safe in a very damp 80-year-old unfinished basement for years and haven't had any problems at all. I have 2 large Golden Rods in it and the humidity, as measured with a $20 digital thingy from Radio Shack, often runs in the 60 to 80% range.

I'll admit to running a 3.5-gallon-tank dehumidifier when there's water pooled on the basement floor from torrential downpours, but other than that the only heat is from the gas-fired boiler and the radiator pipes running around the ceiling. Normal wintertime temp in the basement is 55* F. No AC down there either.

Even scrap gunmetal, like the end I bobbed off my BHP hammer a few years back, hasn't rusted and I degrease it with Gunscrubber before I toss it on a shelf.

Now you know why good oil and/or a light coat of RIG is my friend.

And forget dessicants, I tried a bit box (sold for gun safes) and a big tub (made for drying flowers) and they saturated in a matter of days.


January 3, 2007, 09:25 AM
If you have any wood stocked guns, that is. Going from excessively dry to a humid day at the range or on a hunt in damp weather and then back again, could (I said “could”), over time lead to cracking, or over the short term, a change in point of aim. I don’t want to get too crazy here, but depending on the how well your stock is sealed, it could be anywhere from a non-issue up to pretty bad

January 3, 2007, 09:28 AM
I dont have a gun safe, but i do have a large construction type steel tool box . My dad always used a small salt lick placed in an aluminum pie pan in the bottom of the box. and replaced it every so often as needed. You all know what happens to salt when it gets damp.

January 3, 2007, 10:11 AM
Live on a salt water canal in SW Fla. Keep most of my guns in the gun safe in the house. I do not use a Goldenrod or light in the safe and do not have any rust problems. Of course the house is AC'ed and that helps with the humidity.Just checked and outside is 75% and inside was 60%. I have used Breakfree for years and still do.

January 3, 2007, 11:32 AM
40% is ideal for the wood. Less than 20% is ideal for the metal. Sort of a conflict. Properly cared for, 40% won't cause problems with the metal so shoot for 40%.

Seldomn thought of danger with very low humidity. If you build up a static charge and a spark jumps to the gun metal it will puncture the blueing and leave a microscopic pinhole as a potential place for rust to start.

Keep leather, lamb's wool, etc. away from stored metal. Allow some breathing unless you are packing in cosmoline or equivalent.

Breakfree is NOT the best preservative. It gums up and has no rust inhibitors. As the name implies, it's meant for freeing up stuck things.

January 3, 2007, 01:51 PM
"It gums up and has no rust inhibitors."

WHAT? That's not true. Let's look at the manufacturer's site:

"Corrosion inhibitors prevent the formation of rust while Break-Free's unique boundary film protects metal surfaces from moisture and other contaminants."

January 3, 2007, 02:04 PM
Breakfree is a top notch rust preventative and always seems to rate near the top on the many dozens of informal preservative tests I have read on these sites over the years (usually steel plates, iron nails, etc treated with a variety of oils and greases, then placed in very humid environments for weeks on end). BTW, WD-40 usually seems to rate near the bottom on these tests (maybe you are confusing the two).

January 3, 2007, 02:12 PM
I've had no problems with rust, either, but I'm pretty religious about making sure that metal gets oiled. I do have dessicant packs in the safes, but I've never really noticed them getting saturated. The indicator cards never either they never get saturated, or they get saturated right away. Hmm.

The basement in general is hovering at about 40-45% humidity, but I do have a dehumidifier running. I'll check what it is in the safe next time I'm in the basement.


January 3, 2007, 02:16 PM
Your conditions sound just fine.

January 3, 2007, 02:23 PM
20% humidity is like being in the desert. It's pretty darn dry!

January 3, 2007, 02:54 PM
I was just outside and thought it was as dry as I've seen it in quite some time. Not a cloud in the sky and perfect weather.

I just checked: 58*F and 39% humidity. Arrrgghhh, dry skin, nosebleeds, static cling. :)


El Tejon
January 3, 2007, 03:07 PM
My safes are kept at 30% humidity and have been for many years.:)

Never had a problem with synthetic stocks, wood or metal. All weapons are always wiped down after handling, doubly so if women handle.

Car Knocker
January 3, 2007, 03:19 PM
20% humidity is like being in the desert. It's pretty darn dry!
I just checked: 58*F and 39% humidity. Arrrgghhh, dry skin, nosebleeds, static cling.
Another 2 or 3 months and we should be back to single-digit RH. I've seen it as low as 3% in March. Can't stand that Equitorial jungle humidity some of you folks put up with.

January 3, 2007, 03:42 PM
Hatcher's Notebook has a whole chapter on "Gun Corrosion and Ammunition Developments." I think that's where you read the 50% humidity deal, but this was with respect to firing corrosive ammunition. or salt deposited by other means... like fingers.

Don't have much of a problem with it here in CO where it's usually pretty dry --as a poster said, "nose-picking" dry. Makes yer eyeballs shrivel up, too.

Oh. And the static. There are times when I've reached for a light switch and I've felt like a thunderhead cloud.


Biggest problem out here, usually, is bringing in a cold hunka metal to indoors. Condensation, you know.

January 3, 2007, 06:29 PM
Where I come from it's 95% RH and up. Pussies. :neener:

January 3, 2007, 06:54 PM
I don't remember all the specifics, (been a long time) but the answer is a combination of humidty and temperature.

The warmer the air the more water (i.e. humidity) the air can hold. In other words if you raise the temperature of an area and the amount of water in the air remains the same, then you have lowered the relative humidity (the actual amount of water in the air divided by amount of water the the air can hold at that temperature).

The trick is to keep the temperature above the dew point.

I believe this is how the Golden Rods work, they keep the air in the safe a slight bit warmer than the air surrounding the safe, so the relative humidity inside the safe is lower than that outside the safe.

I have a friend who has kept guns in a safe in an outside garage for more than 10 years with no rust using Golden Rods. This in an area of the country that can easily see 90%+ humidity.

January 4, 2007, 09:06 AM
3%? Does your spit evaporate before it hits the ground?

The weather here is nice this morning. It's 50*F and 81% humidity.


January 4, 2007, 09:32 AM
Humidity by itself isn't the problem. The problem comes when the surface temperature drops to the dewpoint causing condensation to form on your guns however slight.

A low watt light bulb or Goldenrod in your safe along with a dessicant or VpCI emitter and routine maintenance will keep the rust monster away.

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