Useless gun information: (for those more knowledgable please correct)
Most large bullets can't pierce armor because they are flat or ball tipped. They have a ton of stopping power and can blow through flesh but that's mostly the gun working. Certain bullets are nasty(specifically the soft tips) because they flatten on impact and enlarge the wound.
Armor piercing rounds are usually for rifles which are smaller or are particularly sharp tipped. They have less stopping power but more piercing power. So the impact may not make someone fall but the resulting wound will.
The stopping power would mean if you have armor, it may not go through but it feels like being punched by a boxer. I think
