If you're at the range and something goes wrong, stop. This video isn't new, but it captures something important. About halfway through, the shooter has a squib. I would guess that the projectile is just partway into the barrel and is still partially in the chamber. The shooter does not recognize what has happened. He manually ejects the spent case and inserts a live round. This is his opportunity to prevent what is coming. If he had paused to ask himself why the empty case had not ejected, even if he didn't notice the light response, he could have checked the barrel.
Instead he loads another live round and attempts to fire. The rifle does not fire because it is not fully in battery. He hits the forward assist, then ejects that round, checks his magazine, and loads another round. This was his second opportunity to fully assess the problem.
This round doesn't fully go into battery either. He strikes the forward assist again, this time managing to get the rifle into battery, likely by pressing the bullet back into the case, and pulls the trigger.
If you ever have a round that doesn't cycle the action, that is a clue.