A number of BE weapons are lacking idle animations. This includes the assault rifles, scout rifle and SMGs. All NF weapons have idle animations already. Not really a bug, idle animations are a feature more than anything else, so I'm dropping this here.
Are you thinking of anything fancy that plays after a while of not doing anything or do you mean just the average sway?
I think Candles means a simple idle animation when the player is not moving his mouse. When you move around with the mouse, the weapon sways towards that direction, I think that part is in code.
You could just copy and paste the animation from nf to be. I mean if it's weapon sway, that's what I would most likely do.