What Causes Ammunition Corrosion and How Can You Prevent It?
Quick Answer
Ammunition corrosion is usually caused by moisture combined with oxygen, salts, chemical residue, or other contaminants. Temperature swings can create condensation, while damp cardboard, water exposure, skin salts, cleaning chemicals, and humidity-trapping storage materials can accelerate deterioration.
- Brass or copper: Watch for green or blue deposits, crust, and pitting.
- Steel: Reddish-brown rust or a rough surface can indicate active corrosion.
- Aluminum: White, powdery deposits or pitting deserve attention.
- Cosmetic tarnish: Smooth, even discoloration may be harmless, but cartridge condition and storage history still matter.
Prevent corrosion by keeping ammunition in a cool, dry, temperature-stable location. Retain the original packaging for identification, then place it inside an appropriate sealed storage container. Use humidity indicators or desiccants according to their manufacturers’ instructions, and inspect stored ammunition periodically.
Cartridges with heavy deposits, pitting, cracks, deformation, corrosion around the primer or case mouth, or an uncertain water-exposure history should not be used. Do not attempt to restore questionable ammunition with oil, solvent, polish, tumbling, or heat. Ask the ammunition manufacturer for guidance when condition is uncertain.
What Causes Ammunition to Corrode?
Humidity, condensation, and water
Moisture starts many corrosion problems. A cartridge stored in a damp room may remain exposed to elevated humidity, while repeated movement between warm and cold environments can produce condensation. Cardboard packaging and some open-cell foams can retain moisture, keeping it close to cartridge cases longer than expected.
A sealed container can reduce exposure, but it cannot remove moisture already trapped inside. Placing damp ammunition or packaging into an airtight box may preserve the damp environment rather than solve it.
Salts, chemicals, and storage materials
Fingerprints can leave salts and oils on cartridge cases. Chemical vapors from solvents, cleaners, or other stored products may also react with metals or affect cartridge components. Leather and moisture-holding foam are poor choices for direct, long-term contact with ammunition when environmental conditions are not controlled.
Case material affects how corrosion appears. Brass and exposed copper can develop green or blue deposits, steel can rust, and aluminum may form a white oxidation layer. Nickel-plated cases can discolor or show damage where the plating is worn, but discoloration alone does not establish that a cartridge is unsafe.
How to Tell Tarnish From Damaging Corrosion
Minor tarnish is generally smooth and limited to a color change. Active or advanced corrosion is more likely to have texture, loose deposits, flaking, roughness, or visible pitting. Packaging condition provides useful context: staining, mildew, a musty odor, or water damage suggests the cartridges need closer evaluation.
- Usually cosmetic: Smooth, even discoloration with no crust, cracks, deformation, or pitting.
- Questionable: Unknown storage history, damaged packaging, isolated rough areas, or evidence of moisture exposure.
- Not suitable for use: Deep pitting, cracks, case deformation, heavy deposits, corrosion around the primer or case mouth, or a loose or visibly displaced projectile.
Do not scrape or polish corrosion to make a cartridge appear serviceable. Surface cleaning cannot reveal whether deterioration has weakened the case or affected the primer and propellant. Follow the ammunition manufacturer’s recommendations, and check current federal, state and local law when arranging disposal.
Safe-handling reminders: Treat every firearm as if it is loaded. Keep the muzzle pointed in a safe direction.
How to Prevent Ammunition Corrosion
- Choose a stable location. Avoid storage areas subject to persistent dampness or major temperature swings. A climate-stable indoor location generally makes moisture control easier.
- Keep identifying packaging. Original cartons preserve caliber, load, manufacturer, and lot information. Place those cartons inside suitable products from the Cases & Storage category rather than dumping mixed cartridges into an unidentified container.
- Control and monitor moisture. Use an appropriate humidity indicator or desiccant according to its manufacturer’s instructions. Desiccants require inspection and eventual replacement or reactivation; they should not be treated as permanent protection.
- Keep chemicals isolated. Do not coat cartridges with oil or solvent. Store ammunition away from products in your Cleaning & Maintenance kit so leaks and vapors are less likely to affect it.
- Inspect periodically. Look for changing color, deposits, damaged packaging, or moisture inside the container. Keep lots labeled and use older serviceable factory ammunition before newer stock.
Ammunition kept in magazines also deserves periodic visual inspection for corrosion or contamination. Follow the firearm and magazine manufacturers’ instructions for inspection and maintenance.
What to Do After Moisture Exposure
If ammunition or its packaging becomes wet, treat its condition as uncertain. Separate the affected lot for evaluation and record the manufacturer and lot information. Heat drying, chemical cleaning, tumbling, and polishing are not reliable restoration methods for loaded cartridges. Contact the ammunition manufacturer for product-specific guidance.
Reloading components also need dry, stable storage. Primers, propellants, bullets, and prepared cases should remain in properly identified packaging and be managed according to component and equipment manufacturers’ instructions. Shoppers who assemble their own cartridges can browse Reloading equipment and storage-related supplies.
If corrosion or residue is found inside a firearm, follow the manufacturer’s maintenance directions. Before cleaning or inspecting a firearm, unload it, remove the magazine, lock the action open, and visually and physically check that the chamber is empty.
For factory-loaded cartridges and storage-ready options, browse the BT Gun Company Ammunition category and choose loads that match your firearm manufacturer’s specifications.