You empties are spinning on the way out of the ejection port slapping the case mouth against the reviever. I see it a lot with ARs with gas or buffer out of whack. You are likely slapping the bolt handle to the rear on extraction .

 

Aliens

 

On multiple rifles? Do you wear jewelry or something else that could do that?

 

Thank you for the replies. Im trying to help solve a mystery for a friend. He mentioned he does catch the spent case when it ejects. I suggested maybe something in the carrying case or maybe a pocket on the outside with something that is poking thru. Im waiting for his confirmation. I also asked if he wears a watch or bracelet on his right hand, he said no.