Ammo is a stat that dictates the maximum number of bullets that can be stored and fired from a weapon. As the weapon is fired, the number of available bullets decreases from the maximum to zero, at which point no more bullets can be fired. Weapons can be reloaded to regain bullets up to the maximum.
Ammo Scavenger additional increases Ammo by +2 Per Soul secured or denied from an entity.
Melee Charge has a chance to either reload the player's weapon instantly or give up to +100% bonus ammo when hitting a Heavy Melee attack against an enemy.
Map spawns
Golden Statues can provide a permanent increase: +4% Ammo before 10 minutes, or +6% Ammo before 25 minutes, or +8% Ammo after 25 minutes.
Power up runes can provide a temporary Gun buff that provides +40% Ammo for 160 seconds.