Thread: Rings on cartridge 303

I recently aquired a sporterised 303 and gave it a bit of a birthday before getting it looked over by someone who knows them very well. He reckoned it should be good to go, so I put a few rounds through it using the string on the trigger and hiding behind the longdrop technique. All good.
Put a few more rounds into a taget at 50 meters and still all good.
Then I noticed that the spent shells had a faint ring around them, which you can hopefully see in the pic.
Is this anything to be concerned about, IE too much pressure ??
Ammo used is Winchester super x 180gn pp