I picked up some 9mm brass after a local USPSA match. Some of the brass has vertical serrations on it. It reminds of .308 brass fired in a H&K rifle. The serrations are not very deep and almost undectable by feeling the case. The noticeable lines are from the escaping gas that causes a dark lines down the brass.
My question Is there a pistol or pistol caliber carbine that uses a fluted chamber? Or could it be caused by roll sizing the brass? This was reloaded cases.
Just curious as I have never seen this before on 9mm brass. Any percautions about reloading the brass?