You recently wrote: “Oxygen absorbing packets would have no efficacy for ammunition storage. (These are designed just for killing insect larvae in storage foods).” Sorry, Jim, but that’s not quite correct. Oxygen absorbing packets come in a variety of sizes and do their job very well. Their job? Absorbing oxygen. They are placed in packets of food such as jerky to reduce amount of oxygen which degrades the flavor of the food. That they also make life more difficult for bugs is a side-effect.
The ability to absorb nearly all the free oxygen in an enclosed space makes them uniquely qualified for preservation of a variety of things – including guns and ammo. Back when Y2K  was the big issue, I enclosed an SKS  [carbine], a hundred rounds of ammo and several oxygen absorbing packets in a plastic tube with and glued-on caps. I stored it outside for a year before I opened it up to check it out. When I made my initial cut into the pipe I was rewarded with a “hiss” as air entered the pipe. Since oxygen comprises about 16% of our sea-level atmosphere and since it was now tied up in the packets I was left with a partial vacuum inside the pipe. Upon reassembling the rifle, I loaded it with the ammo it had been stored with and fired it.
I need to point out that this experiment was conducted in Oregon, a fairly wet climate, and that after close inspection of the rifle, I found no rust on any of the metal. Obviously, oxidation of the steel couldn’t occur when the oxygen wasn’t free to combine with the iron. – D.Y.
JWR Replies: I should have been more thorough in my reply to that letter, when I mentioned Oxygen (O2) absorbing packets . Instead of dismissively writing “…have no efficacy for ammunition storage” I should have written “…are not the best choice for ammunition storage”. (I will update that post.) I will elaborate:
If you are the “belt and suspenders” type, then by all means use both desiccant packets (such as silica gel) and O2 absorbing packets. But of the two, desiccants are much more reliable. The formation of rust takes two ingredients interacting with ferrous metals: moisture and oxygen . Ditto for oxidation of copper and brass. Without moisture present, corrosion will not occur with typical atmospheric oxygen levels. Hence, O2 absorbers are not “uniquely qualified”, as you asserted.
Both types of packets will work in protecting guns or ammunition is sealed containers, but desiccants have far more reliable efficacy. The biggest problem with typical food grade O2 absorbing packets is that there is no easy way of insuring that they were handled properly before they came to you. The O2 absorbing packets that I have seen all have gas-permeable coverings. If the seal on the outer package that the packets were shipped in was compromised, or if they were removed from their original packaging and later re-packaged, then they will have virtually no usefulness. They are effectively “used up” when they come in contact with a large volume of air for more than a few hours. And once used, these packets cannot be reactivated at home. You have to buy new ones.
But unlike O2 absorbing packets, if you use silica gel desiccants, you can reactivate them by simply putting them in a dehydrator (or in a kitchen oven on a 150 degree F setting) overnight. Using this method, they can be used over and over. This is vastly superior, especially in the context of a survival situation where regular commerce is disrupted. And, as I’ve mentioned previously in SurvivalBlog, in the present day, desiccants are often available free for the asking. Just make a few phone calls. Piano shops often get musical instrument shipments that include large desiccant packs. Most of these get thrown away.
So if you are going to depend on one of the other for firearms and ammunition storage, in my opinion you should choose silica gel desiccants rather than O2 absorbers. OBTW, beware of re-using any packets that you find in jerky packaging. These sometimes include an integral moisturizing packet, to prevent jerky from becoming too dry. Those packets would of course be counterproductive, for ammunition or gun storage. Again, only use O2 absorbing packets that are factory fresh, and preferably that come vacuum shrink wrapped. Otherwise, you have no way of knowing whether or not they have already been chemically neutralized.