Many of these weapons come from the standalone mods available for this game. Aiming down sights is ill-advised for close encounters due to the strong recoil, and with the proper mods it can be made quite accurate for firing from the hip.

While in Fallout 3 this was limited to the creation of custom weapons, New Vegas takes this a step further by allowing the creation of weapon variants based on basic weapons by adding weapon mods.

11.2MB 24.3k- Desert Eagle - Standalone Handgun. This mod delivers the R9 assault rifle to Fallout 4, along with custom textures and meshes. This is the gun that you want to have in your fight against your enemies. Rumors that a legendary RU556 Assault Rifle has been spotted in The Commonwealth, apparently a ship from before the war was carrying an illegal prototype. Unlike previous installments, weapons in Fallout 4 fall under three classifications: normal, legendary, and unique. You can use this as a lightweight to medium weapon with the automatic firing capability.

Fallout 4 standalone weapon mods