The rule is: there is no such thing as an unloaded gun.
Consider that all guns are loaded at all times, then handle appropriately.
That prevents a lot of ‘stupid’ accidents.
My dad did allow that a totally disassembled firearm was “probably” unloaded. Once you began reassembly it becomes loaded again. He was a stickler about the rules but I guess that is natural enough. He taught weapons for a brief period during WWII. I wish I could have taken his courses: Ma Deuce and heavy mortar.
There are such things as unloaded guns. It is up to the person holding it to know if it is or is not loaded. It isn’t hard to check, and there is no excuse for not knowing with absolute certainty.
You should assume loaded until you personally have proven beyond a doubt it is not. The only safety on a gun is the person holding it.