You can expect well-stored ammo to last 50+ years stored in Mylar bags as long as you keep moisture away from the cartridges. I wasn’t sure if Mylar would work for ammo, so I researched. Here is what I learned.
Mylar protects ammunition from oxygen, water, light, vapors, and chemicals. When sealed, it provides a waterproof ammo container for your bugout bag and cache storage locations. It is excellent for organizing bulk ammo—Store Mylar bags in a rigid container to protect them from physical damage.
To protect ammunition in Mylar bags,
- Place a desiccant packet inside the bag before sealing it
- Store the Mylar bags inside a protective outer shell such as a .50 cal ammo can or a rigid plastic container.
Storing ammo this way may seem like overkill, but if we’re talking about bulk survival ammo, it isn’t. Decades of storage life come at a price. Taking the extra time to put ammo in Mylar removes some of the risks related to moisture-induced ammo degradation.
If you are shooting thousands of rounds at the range, practicing CCW, or hunting, storing ammo in Mylar may be overkill…but there is more to Mylar than keeping moisture at bay.
11 Things To Think About When Storing Ammo In Mylar Bags
Mylar isn’t just good for protecting bulk ammo from the elements; it’s also an inexpensive way of organizing large volumes of ammo into manageable amounts. If you are considering Mylar, here are 11 things to consider.
#1 Mylar Is Waterproof Storage
- Mylar is waterproof. When you seal ammo inside with a desiccant, there shouldn’t be any moisture coming into contact with your ammunition.
Tip: Remove the cardboard and styrofoam packaging materials before packaging in Mylar. They soak up and hold moisture.
- Mylar will keep moisture out, but it won’t get rid of water in the sealed bag. To remove this moisture, place a desiccant inside before sealing.
#3 Types of Desiccant For Ammo
- Silica gel packets-the best option, preferably the “indicating type” that changes color when they have absorbed all the moisture they can.
- Dry White rice
- Cat Litter (clay or silica) Clay is effective in a low-oxygen environment
#4 Light Protection
- Mylar acts as an excellent light barrier keeping out Ultra Violet light that can degrade ammo over the years.
#5 Flexibility and Organization
Place any number of rounds into a Mylar bag to fit your needs. I plan to store packets of 50 and 100 rounds. This seems like a manageable amount of ammo for placing in my range or bug-out bag.
#6 Limit Exposure
Packaging a small number of rounds in each Mylar bag limits how many cartridges are exposed to humidity. Did I mention I live in Florida?
Every time I open an ammo box, I expose all of the ammo in the box to remove 50 or 100 rounds. If rounds are pre-sealed in Mylar, none of the cartridges are exposed until opened.
#7 Repackaging Ammo
- The only thing cardboard does for your ammo is keep it from getting scratched during transport.
- Remove cardboard packaging and styrofoam from ammunition before storing.
#8 Easy Labeling
It’s easy to mark specific batches of ammo because you can write directly on the Mylar.
With a permanent marker write:
- The caliber and type of ammo
- Take notes on performance.
- Cartridge load information
- Reminders and messages to yourself, i.e., “never buy this ammo again.”
- If there is enough room to reseal, the Mylar can be reused
#9 Store Inside A Rigid Container.
Mylar isn’t nearly as tough as a .50 cal ammo can. Consider storing Mylar bags inside a rigid container like a metal ammo box or a plastic lidded container. I store mine in a lidded 5-gallon bucket when in bulk and transfer it to a small lidded plastic container in my bag(s).
Tip: Disguise your ammo from thieves by packing it in paint cans or other storage containers that don’t scream, “ammo for the taking.”
This will help keep the Mylar from being damaged, keep things organized, and make for easier storage.
#10 Heat and Fluctuations In Temperature
- Mylar doesn’t protect ammunition from heat or fluctuations in temperature.
- Avoid storing ammunition in areas without temperature control, such as a garage, attic, crawl space, or outdoor shed.
#11 Don’t Use Oxygen Absorbers With Desiccant
If you plan on using Oxygen Absorbers with Silica Gel desiccant, don’t. Silica Gel works poorly in containers with low Oxygen concentrations.
Check out this chart on the properties of various Absorbents
|Property||Molecular Sieve||Silica Gel||Montmorillonite Clay||CaO||CaSO4|
|Absorptive Capacity at low H2O Concentrations||Excellent||Poor||Fair||Excellent||Good|
|Rate Of Absorption||Excellent||Good||Good||Poor||Good|
|Capacity for Water @77° F, 40% Relative Humidity||High||High||Medium||High||Low|
Desiccant: Ammo in Mylar bags
Fifty cubic inches of ammo storage space requires 1 gram of silica gel desiccant. For example, a one-gallon Mylar bag is approximately 231 cubic inches in volume, so you need 4.6 grams of desiccant. Packets come in a minimum of 1 gram, so you need five 1-gram packets.
For a 5-gallon pale lined with a Mylar bag, you would need approximately 23 grams of desiccant.
You can purchase silica gel packets in all different sizes, so determine the size Mylar bags you will use before purchasing desiccant. I prefer using the 5-gram packages and more desiccant than needed.
When I store 50 or 100 rounds in a one-gallon Mylar bag I cut it down but I know if I use 5 grams of desiccant I’m good to go.
Tip: For storing ammo, I would avoid purchasing the 1-gram silica gel packets and jump up to the 5-gram packets. You will use a little extra, but they are more flexible for ammo-sized containers.
Tip: Remember that cardboard packaging and styrofoam hold excess moisture, so if you keep cartridges in cardboard boxes, add extra desiccant.
Chart #1 Desiccant: Units per Ammunition Container Size (Clay or Silica)
|Square Feet||Square Inches||Gallons||Cubic Feet||Cubic Inches||Desiccant Required 1oz. units |
(28 Grams Per Unit)
Formula to Figure Ammo Container In Cubic Inches and Desiccant Requirements (ammo in Mylar bags)
Multiply length times width times height equals the number of cubic inches in a container. You need 1 gram of desiccant for every 50 cubic inches so divide the total cubic inches by 50 for the grams of silica gel desiccant required.
Length in inches x Width in inches x Height in inches = Cubic Inches
Example #1 Container
12″ x 12″ x 12″ = 1,728 Cubic Inches
1728 ÷ 50 = 34.56 (grams of silica gel desiccant required)
Example # 2 50 Cal. Ammo Can
10.75″ x 5.5″ x 6.75″ = 399.09 Cubic Inches
399.09 ÷ 50 =7.98 (grams of desiccant required)
When you do the calculations, round up to the subsequent whole gram because desiccant packs come in even increments.
How do you Store Ammo Long-term?
The military stores bulk ammo in sealed metal containers in climate-controlled buildings. You can do the same thing by keeping ammo stored in a cool, dry location like an indoor closet.
Tip: Rotate Your Ammo if you are storing ammunition for CCW, you need it to be reliable; it’s a good idea to shoot through specialized ammo every 6 months to a year. This way, you know your ammunition will be reliable in an emergency.
Mylar VS Vacuum Bags For Ammo (ammo in Mylar bags)
Vacuum bags are pretty tough, but they allow moisture and oxygen transfer. Vacuum bags are not a good option if you are going for long-term storage of ammunition, i.e., decades of shelf-life.
Should I put O2 Absorbers and Desiccants Together In Mylar? (ammo in Mylar bags)
Oxygen absorbers need moisture, and Silica Gel Desiccant packets don’t perform well in an Oxygen-free environment. By using both in your ammo storage container, you are canceling the benefits of both. It will be like you didn’t put anything in the storage container.
Ammunition doesn’t need to be protected from Oxygen, but some owners like the vacuum-type seal they can provide.
Because Moisture is the number one corrosive for Ammunition, you are better off going with just Silica Gel Desiccant and a well-sealed Mylar bag or sealed ammo can. Skip the Oxygen Absorber altogether.
Should I Vacuum Seal Ammo Storage
As already mentioned, the only thing that kills your ammo is corrosion due to moisture. You want a desiccant in the container to remove moisture.
Silica gel packets are the most convenient desiccant, but they perform poorly in an oxygen-free or vacuum-sealed environment. If you have to vacuum seal, use the Montmorillonite clay mentioned below, it does a better job of removing moisture in an O2-free zone.
Use Montmorillonite Clay As A Desiccant (ammo in Mylar bags)
If you plan on storing ammunition vacuum-packed or in an Oxygen-free container, use Montmorillonite clay instead of silica gel packets. Clay is effective at removing moisture in an O2-free environment, silica gel is not. (see chart above)
Make Your Own Desiccant Packs
Storage Tip: Make your own clay desiccant packets with coffee filters and cat litter made from Montmorillonite clay. Simply pour the litter into a coffee filter and staple it shut.
If you have any suggestions, leave them in the comment section below.
Keep on prepping.