This bug seems to be tied to specific guns spawned in on the world, or possibly brought into other servers from looting another one?
Some guns don't produce gunshot sounds for others in the world, and it seems like a widespread bug. We're probably missing out on lots of instances of people having gunfights, yet we can't hear the gunshots because of this.
Please prioritize this, and hit reg fixes soon.
(also, no gunsmoke or bullet trails coming from the gun after he sprayed his magazine into the air, at the end of the clip?)