Yes. Damp foam can keep moisture against a firearm, and closing the case can slow drying. Water can arrive with the gun even when the case itself has kept the weather out.
Browning advises removing firearms from their cases after hunting or shooting, and warns about condensation in tightly sealed cases. If rust has appeared, check whether the padding beneath that area is damp. [1]
Check for moisture where the rust appeared
Completely unload the firearm and verify that the chamber is empty before inspecting it. Remove it from the case and examine the surfaces that rested against the padding. Then check the foam beneath those areas for dampness.
With removable foam, lift it out and inspect the underside and the bottom of the case. Moisture can remain below the surface even after the exposed padding feels dry. Leave the case open and let damp foam dry separately at room temperature, with the firearm securely stored elsewhere.
After a wet outing, clean and preserve the firearm before putting it away for an extended period. Browning recommends a very light coat of gun oil followed by a thorough wipe-down. Once the metal is prepared, minimize direct handling of those surfaces before storage. [1] Our long-term storage guide covers preparation and inspections.
When the foam itself is deteriorating
Replace foam that becomes sticky or starts crumbling. Deposits from deteriorating plastics can stain surfaces they touch, and some aging polyurethane foams release acids that corrode metal. [2, 3] For replacement padding, look for closed-cell polyethylene, a water-resistant material used in protective cases. Water can still collect on its surface or underneath it, so dry the case before repacking. [4, 5]
Check again after the firearm warms up
A cold firearm brought into warmer, humid air can collect condensation. Dew point is the temperature at which the available moisture can begin condensing; metal below that temperature can become wet even when the room’s relative humidity appears moderate. [6]
An immediate wipe on arriving indoors may happen before all the condensation has formed. Inspect the gun again as it warms before putting it away for an extended period. Check the padding that contacted it as well. Leave damp equipment out of the closed case to dry, with the firearm securely stored during that process.
Measure inside the case
A room’s humidity reading doesn’t show what is happening beside the firearm inside a closed case. Choose a temperature-and-humidity monitor with saved readings, small enough to fit without pressing against the gun.
Keep the sensor openings exposed to the air. Start with a week of recording in the location where the case will be stored, and review the history each day. Recheck after a wet outing or during wetter seasonal weather.
For a stable mixed collection at normal indoor temperatures, 40–50% RH is a useful working target, unless the firearm requires different conditions. [7] Our gun-safe humidity guide explains the target and how to select a monitor with a history graph.
If humidity remains high inside the case while the room is drier, inspect the padding again for retained moisture. If the room’s humidity is high too, choose a drier storage location or use room-level dehumidification. Drying the room reduces the moisture introduced whenever the case opens.
Once the case and firearm are dry, desiccant can help manage water vapor in the closed space. Service it according to its indicator and instructions, and keep checking the recorded conditions. Dry padding gives the material less moisture to handle. [8]
A compact option that stays with the firearm
XeroMag is designed to take the place of a compatible firearm’s magazine during unloaded storage. Its compact format keeps the storage accessory with the gun inside the case, without needing space for a bulky separate unit beside it. Activated alumina desiccant takes up water vapor, alongside a separate Cortec VpCI-170 corrosion-inhibitor element. It works without electricity or batteries.
The removable baseplate lets you replace both consumables and keep using the insert. A separate Desco indicator card provides a visual humidity check when you inspect the case. Choose the listed XeroMag configuration for your pistol or AR-15-pattern firearm, and check that the case closes normally with it installed.
Sources
1. Browning: How should I store my firearm?, case storage and preservation.
2. Society for the Preservation of Natural History Collections: Storage Materials—Plastics, degradation deposits and acidic emissions.
3. Canadian Conservation Institute: Products Used in Preventive Conservation, Technical Bulletin 32, Polyurethane subsection and contact-damage table.
4. Pelican: Custom Case Solutions, polyurethane and polyethylene foam characteristics.
5. Sealed Air: Ethafoam polyethylene foam, water resistance.
6. National Weather Service: Dew Point vs. Humidity, dew point and condensation.
7. Canadian Conservation Institute: Storage of Metals, CCI Notes 9/2, stable mixed collections.
8. Canadian Conservation Institute: Preparing silica gel for contained storage of metal objects, monitoring and servicing.
[…] Take the firearm out and inspect beneath the padding. Leave damp padding out to dry at room temperature, with the firearm securely stored elsewhere. If rust follows the points where metal rests against foam, see checking a foam-lined case for retained moisture. […]
[…] Let a damp holster or case padding dry separately while the pistol remains securely stored. Browning advises removing firearms from their cases after hunting or shooting. [4] For checking moisture beneath padding, see Can Guns Rust in Foam-Lined Cases?. […]