Occasionally a customer contacts me with concerns about primers being slightly dimpled upon chambering a round. This is completely normal and is a characteristic of all basic AR15/M16 rifles. The firing pin in an AR15 is free floating inside its chamber. The forward inertia of the bolt upon chambering a round causes the firing pin to bounce forward with just enough force to leave a small mark on the primer. This is never enough force to cause a slam fire in an AR15 though. I do recommend rotating the rounds though when un-chambering and re-chambering rounds frequently. And as always have the rifle pointed in a safe direction at all times.