I'm far from an expert, but I'll give it a shot. I do want to say I'm very careful about gun safety hunting. My dad always taught me... Never point a gun at something you don't want to kill. Never hand someone a loaded firearm. Treat every gun as of its loaded. (he taught me alot more than that, but you get the idea)
1- from my understanding if dropped a discharge is possible but rare, and even more rare in modern firearms.
Perhaps if your "buddy" did a trigger job or something making the gun faulty it would be even more likely. A shitty gunsmith fucks up something.
The gun overheats, but that's more the ammo getting hot that the gun magically firing.
2- don't know... If you drop it and try to catch it you could potentially pull the trigger trying to catch it, so I say don't try, it's less likely the gun will discharge from the fall. Just try to get the fuck out of the way.
3- I always make sure the gun is unloaded and look down the chamber from the action. If it's a bolt action rife for instance, I would cycle the bolt, then look in the chamber, then remove the bolt and look down the barrel from where the bolt was.
4- I would think anyone
5- not familiar with this. Sounds like a barrel of sand to safely shoot into.... Sand is very dense and would stop a bullet fast. Don't know for sure.