NEWS | Oct. 7, 2021

Ammunition: Cold Weather Affects Performance

Soldier firing a M4 in the snow
Photo by John Pennell

Soldiers, we told you how ammo performs when it’s hot, and now it’s time to tell you what happens when it’s cold. Keep reading to see how cold weather affects your ammo’s performance.
Although all of you are not snipers, the information in Paragraphs 4-145 to 4-147 of FM 3-22.10, Sniper (Dec 17), discusses how temperature generally affects ammunition ballistics. Air density also affect ballistics of your ammo. Paragraph 4-147 tells you if the temperature drops 20 degrees, it’ll cause the bullet to impact the target lower by one inch per 100 yards, two inches at 200 yards and so on.  
Something else to consider is your weapon’s zero. If the last time your weapon was zeroed the temperature was 90°F and you’re now in freezing temperatures, your ammo could impact the target nine (9) inches low at 300 meters due to temperature and air density. The best way to ensure you hit what you’re aiming at is to zero your weapon again with the ammo you’re carrying in the field and confirm your battle sight zero at 300 meters in the expected weather conditions.
Why confirm the battle sight zero at 300 meters? Because your 25-m zero is meant to get you in the general vicinity of your target out at 300 meters, but doesn't guarantee it. So confirming your zero at an actual 300 meters is crucial.
It’s also important to keep your weapon and ammo dry in extremely cold weather. What happens when you bring your weapon in from the cold? The warm, humid indoor environment causes condensation to form on your weapon and ammo. If you take your weapon back outside with condensation on the ammo, then it’ll freeze and cause serious problems.  For instance, ammo with ice particles on it will not feed or fully chamber properly. That’s why the best thing to do is secure weapons and ammo outside if you’re going indoors for a quick warm up. 
When you’re done with outdoor training for the day, ensure all ammo is accounted for and turned in to the ammo point. Make sure your weapon is clear of ammo and bring your weapon indoors and give it time to warm up to the indoor temperature. Then thoroughly wipe all condensation off the entire weapon, and clean and lube the weapon in accordance with the TM before storing it in the arms room.
Never lube your ammo thinking it’ll keep condensation off. Lubricant on ammo creates more problems, with the most hazardous being excessive pressure against the bolt face. This pressure causes cracks on the bolt locking lugs.  See this PS Magazine article for details:
Remember to report any defective ammo. This PS Magazine article has all the specifics: