Child Actor affecting main character's movement

Hi, there.

Now I try to create FPS game with a long rifle asset. However, when I set the rifle as Child Actor under the fps hands and play the game, the enhanced input for move did not work well (ex. pressing W makes the character move left).

Before I set this rifle as Child Actor, the character moved correctly.

I changed the rifle’s collision setting to No collision and checked the ignore for a pawn, but they did not work.

Finally, I temporarily resolved this issue by putting the rifle a little bit outside the capsule as the second image shows.

I found some similar questions regarding this problem but it seems nobody cleared this question.

If you have any solutions for this, I really appreciate your supports.