Screecher

 is a gun that fires sound waves that grow wider as they travel. The sound waves pierce through enemies and have a small chance to stun enemies and cause them to no longer pay attention to the player, during which they'll be vulnerable to other enemy bullets.

Trivia

 * The gun could be a reference to anti-riot weapons such as the Long Range Acoustic Device (LRAD), which uses a form of non-kinetic and non-lethal form of crowd dispersal. This also appears to be referenced in the Ammonomicon Entry.
 * This gun could also be a reference to the Address Disruptor from Axiom Verge. The shape of the bullets match that of the disruptor, and both not only make rather weird noises, they also hinder enemies in some way.
 * This gun could be a reference to the Pulse Gun from Crimsonland, which made such an annoying sound that players often had to mute their game, "losing their purpose and conviction" in reference to the gun's description. The stun effect is also similar to the Pulse Gun, which confused enemies, except without the added knock-back effect.