Welcome! This is a strange issue that I also ran into with the Enfield. The weapon's other sounds work, but not shooting, right?
The solution I came up with is kind of a cheat; under the weapon's "on_fire_action" section, you can add a sound action of the rifle firing.
If you'd like, I can post a screenshot of that once I get back to my main computer.
Ah I found what you were talking about. However I am not sure what the Lee Enfield sound file is called. So yes, an example would be helpful.