What do armor piercing rounds do in GTA?
They're pretty useless. They do so little damage to light vehicles. They could do with a buff.
Armor Piercing rounds, which ignore body armor and bulletproof helmets, quickly taking down armored players and NPCs alike. It does not affect players equipped with Ballistic Armor. Full Metal Jacket rounds, which improve damage over vehicles and can penetrate bullet-resistant windows.
Rifle armour-piercing ammunition generally carries its hardened penetrator within a copper or cupronickel jacket, similar to the jacket which would surround lead in a conventional projectile. Upon impact on a hard target, the copper case is destroyed, but the penetrator continues its motion and penetrates the target.
Destiny 2 in Depth - Armor Piercing Rounds (More Damage to Shields!)
Armor piercing can one shot a player to the head, if that player is wearing a bulletproof helmet that is. FMJ can shoot through the kuruma's bulletproof glass. If you do PvP, armor piercing. If you hate kuruma trolls with a passion, FMJ.
Body Armor vs Armor Piercing Rounds Test - GTA Online - YouTube
Their color is purple. Explosive: this type of ammo behaves like a small explosive, making it a threat against unarmored vehicles.
A composite metal foam (CMF) material developed by researchers at North Carolina State University can stop ball and armor-piercing . 50 caliber rounds as well as conventional steel armor, even though it weighs less than half as much, the university recently announced.
Some types of modern body armor, mostly used by the military, offer a certain degree of protection against bladed weapons, but far less than medieval armor. Medieval armor would be essentialy useless against a modern high-power pistol bullet.
Armor-piercing ammunition is designed to penetrate ballistic armor and protective shields intended to stop or deflect conventional bullets. Armor-piercing handgun ammunition is federally banned for civilian use or ownership in the U.S. Per 18 United States Code, § 921(a)(17)(B).
What does AP pistol stand for?
The Vom Feuer AP Pistol (Armor-Piercing Pistol) is a weapon in Grand Theft Auto V and Grand Theft Auto Online.
SILVER BULLET made from depleted uranium can pierce even the heaviest armor. Uranium shells burn away at the edges upon impact¿a "self-sharpening" that helps them bore into armor. Used as ammunition, it penetrates the thick steel encasing enemy tanks; used as armor, it protects troops against attack.

But that round is expensive at more than $10 per cartridge, can damage modern small arms accessories like suppressors and muzzle brakes and doesn't hold zero when switching from a traditional jacketed round to the AP round.
Although bullet design is an important factor with regard to armor penetration, the ability of any given projectile to penetrate ballistic armor increases with increasing velocity. Rifle cartridges typically discharge bullets at higher muzzle velocity than handgun cartridges due to larger propellant charge.
A bullet jacket generally 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. In military nomenclature, it is often labeled ball ammunition.
Grand Theft Auto Online
When equipping a bulletproof helmet, they provide better protection than normal helmets, allowing the player to survive lethal headshots.
Tracer bullets are used so you can see where your round is going typcially at night, pretty much useless in GTA.