An ammo backpack is a feeder mechanism and belt or back-carried amoo container linked to a weapon. It provides ten times the usual ammo capacity of the weapon, making reloading largely a ting of the past.
A Suport weapon requires a very large and bulky backpack that prevents you from carrying much else, a nonconcealable weapon requires a rather small backpack and smaller weapons only require a fanny or bet pack that is quite unobtrusive.
AmmoPacks are considered military hardware and rarely used by police or civilians. They cost anitem schtck to get.
It takes three shots to attach or deattack an AmmoPack - less if you have Lighting Reload.