"Brutalizing the extractor"

And yes you can, just like in the video.

Open and lock bolt.

Drop round into chamber.

Release bolt.

What Jerry is saying that when the bolt goes home with no resistance from pulling the round out of a mag it (can) move with enough force that the firing pin moves forward due to its mas, striking the primer and causing a negligent discharge.

While I often drop single rounds into the chamber and let the bolt slam home. I do it with the gun pointed in a safe direction.

Some times i get rounds that have a primer strike and faile to fire. So i remove the mag, drop the single round in and fire it.