The box trace is used to make a series of boxes that go from location A to location B, checking for overlaps along the way. That’s why you have a start and end and box size.
You only need 1 box here, on the sword. So you can just add a box collision to the sword ( socket ) the moves with the sword, and you’re done 
TBH I haven’t coded any combat stuff, so I could be totally wrong here, but I think you’ll find it works 
Maybe, if you have problems picking up collision when moving the sword quickly, you might use a box trace, and it would go from the handle of the sword to the tip, for each frame. But I doubt that would help, and harm your frame rate.