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.
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
Gold Urns can provide a permanent increase: +4% Ammo before 15 minutes, or +6% Ammo after 15 minutes.
Power up runes can provide a temporary Gun buff that provides +40% Ammo for 160 seconds.