Aiming system

hey guys, i’m trying to do an aim system, and i have some doubts: how can i affect the FOV of the câmera just for the weapon (like in here → http://vignette2.wikia.nocookie.net/battlefield/images/a/a1/BF4-FAMAS_Irons-bmp.jpg/revision/latest?cb=20131226160259 ) because when i change the FOV, everything looks closer, but i want the world to be not affected by the FOV, and I want to add some blur only in the weapon

If you change the field of view you change it for everything. If you want to have a different fov for the weapon and the map you would need a second camera that is only rendering the weapon. I bet it is passible in UE4 but i never did it before. Thats why i cant help there, but i thought mb i can give you some ideas what you can research how to do.