Do weapons need to be equipped to the Primary or Secondary slots to function, or can they work while equipped to the Back slot?

I noticed that the Macro Binoculars work no matter what slot they're equipped to so I thought I would see about weapons.

last i hunted they needed to be equipped in Primary or Secondary

The weapon you shoot with is only selected from Primary or secondary Weapon slot. You can still carry a weapon on your back as backup for fast switching :)

Thanks for the help you guys.