Not one bit. I would treat both the same.
neither a barrel by itself or an upper (with or without BCG) is considered a firearm. Just a part of one.
however, I would personally be more aware of where I was pointing the AR upper. I wouldn’t go ‘aiming’ the pistol barrel at anyone either.
so, a bit of a tangent:
I was thinking, what if this was a revolver without an easily removable cylinder or a fixed barrel firearm like a beretta? Can’t handle live or dummy ammo in safe area. Soooo if that was the case I would ask if an RO/or other official was available to Supervise at a vacant bay or see if the chrono folks weren’t too busy. They can issue the make ready to start the process. I could take the slide off, chamber check, reassemble And they could issue proper commands back to the bag or holster. Simple, safe, legal per rules.