Sound Weapon Sound Mutator (for default weapons)

[xlzqwerty1]

How do I include a custom weapon sound to a mutator? Everytime I try to include a custom sound

class'DeagleFire'.default.FireSound = Sound'KF_DeagleSnd1.50AE_Fire';

, it gives an error saying Error, Missing Sound Name?

I am probably doing it incorrectly since I don't know much about coding and functions.

Help is appreciated! Thanks.