From the point of view of an actor and an inventory item working togerther, is there any way to determine if the item is out?

Well any script you have running on the gun will stop running once you're holding it.

If that helps.

From there I guess I could have a timer constantly reset by the gun.

The actor checks the timer, and if it's over something reasonable, it knows it's holding the gun.

Except it'd have to be a global timer so any other instances of the gun would ♥♥♥♥ it up.

The gun sets the timer on the nearest actor with the timer.

As long as the two actors don't get too close, it should work.