On your shells with the dents and scratches in them...
Does it happen on every single one consistently or only on some of them? If every shell has a mark there, you could narrow down where it's coming from. Load the rifle, fire one round, remove the magazine, safety the rifle, and gently eject the chambered round using the charging handle.
If it has the dent/scratch then it's happening before firing or ejection and might be caused by the carrier hitting the shell when stripping or chambering either that round or the round before it.
If the round does not have the dent/scratch then it's happening during extraction or ejection and might be from spinning around and hitting the deflector.