Devil's Trap Bullets
A devil's trap carved into the bullet.
A devil's trap bullet is an ordinary bullet with a pentagram carved onto the tip. It was first devised by Henry Winchester as a way of stopping Abaddon. When someone fires one of these bullets into a demon, it acts the same way as a devil's trap by debilitating the demon and keeping them from moving or using their powers, but it can be removed with some effort. These bullets can even affect a Knight of Hell, but Princes of Hell are immune to their powers. Demons can protect themselves from the effects of the bullets if they are wearing bulletproof vests. The bullets appear to be more effective than a standard devil's trap as they can restrain multiple demons at a distance, as opposed to having to trick one or more demons into stepping into a protective circle.
When Sam is captured by Abaddon, Henry improvises by carving a pentagram onto the tip of a bullet. Henry has the gun hidden under his jacket when Dean trades him and the Box for Sam. Abaddon reneges on their deal and impales Henry with her hand, but he responds by firing the gun under her chin. She is left unable to move or see into Henry's mind. Dean later decapitates her and tells her that the trap will keep her from smoking out and that they will dismember her meatsuit and bury each strip under cement.
After discovering how to cure a demon, Sam and Dean recover and reassemble Abaddon's meatsuit to complete the third trial to close the Gates of Hell. She is still unable to move due to the devil's trap bullet in her head. They leave her alone, after getting a call from Crowley, but she is able to move her dismembered left hand towards her body and use it to remove the bullet, freeing her.
Upon arrival at Eugene, Oregon, Dean arms Sam, Irv Franklin, and Tracy Bell with devil's trap bullets. After Abaddon ambushes Dean, Tracy shoots her six times with the bullets, but they have no effect on her as she is wearing a Kevlar vest.
As a cautionary measure, Abaddon shoots Crowley with a devil's trap bullet. Crediting Henry with the idea, she tells him that he will be left powerless. Crowley is left unable to help Dean when he gets attacked by Abaddon and her demon minion. After she is killed with the First Blade, Crowley uses a knife to gouge out the bullet from his shoulder and his handkerchief to staunch the bleeding.
With the reluctant intention to complete his deal with Rowena to remove the Mark of Cain from Dean, Sam lures Crowley to an abandoned warehouse and shoots him with a devil's trap bullet. He then places a hex bag in Crowley's coat and watches as he starts to feel the effects of the Defigere et Depurgare spell. After brief monologues from both sides, Crowley is eventually able to remove the bullet, destroy the hex bag, and strike back against Sam.
While plotting how to kill their demon target, Dean states that he'll shoot him with a devil's trap bullet. Later, Dean is seen loading his gun with a clip of devil's trap bullets. When Ramiel arrives, Dean shoots him multiple times, but they, along with Ruby's knife, have no effect on him.