A full metal jacket (or FMJ) is a bullet consisting of a soft core (usually made of lead) encased in a shell of harder metal, such as gilding metal, cupronickel or less commonly a steel alloy. This shell can extend around all of the bullet (alternatively termed a total metal jacket round) or, more often, just around the front and sides with the rear lead part left exposed. The jacket allows for higher muzzle velocities than bare lead without depositing significant amounts of metal in the bore. It also prevents damage to bores from steel or armor-piercing core materials. The appearance of FMJ ammunition is highly distinctive when compared to hollow-point or soft point bullets.
There are some disadvantages to jacketing a bullet. For instance, full metal jacket bullets have different behavioural properties, both inside the barrel of the gun and also in flight. Whereas hollow point and soft-tipped bullets are designed to expand upon impact, metal jacketed bullets have a very limited capacity to expand. This generally makes the bullet pierce through a soft target, often leading to less severe wounding, and possibly failing to disable the target. Hollow point and soft tipped bullets are for use against soft targets only, such as animals or people, whereas full metal jacketed bullets can be used effectively against both soft and hard targets.
In Insurgency, standard ammo is the default ammo provided to the player's weapon if no ammo attachments are choosen. The game assumes that the standard ammo for the player is full metal jacket ammunition. Using standard ammo will not modify bullet damage multipliers, as it is the regular ammunition.