This one is going to help implement a very very simple ADS system where the player can aim down the sights of a gun for better accuracy. First off you are going to want to make this blueprint right here.
You want to add the bool variable (with default being false) for later. **Note getting the gun to come up to the camera view is an animation issue. Just animate the gun going up to camera.
Next we add onto the FPS template spawn projectile blueprint.
This will give you a slight bullet scatter on the zAxis when you are not aiming down your sights. To increase bullet scatter simply increase the range that your random stream variable is plugged into. It also helps to increase your projectiles velocity above what the standard template gives.
If you have any questions feel free to ask!