I dunno about IL, but in CA you would have trouble, I think. Ammo and a weapon can be in the same range bag, but the weapon must have a lock on it or be in a locked hard case. An alternative is to put the weapon the trunk with the ammo in the passenger compartment, but with handguns I use a lock hard case to avoid any possible trouble.
The impediment of having to assemble the weapon would not be enough here.
Seems like parts of IL are as itchy about things as CA is, maybe the reasoning has been applied there.
Loyalty to petrified opinions never yet broke a chain or freed a human soul in this world — and never will.
— Mark Twain