Hi Guys, names Sam. I'm Australian born, but moved to the US for work, and don't think ill be going home. My father was American so i hold a dual citizenship. For Christmas i was given my first ever gun. Its an 870 marine magnum and i LOVE it. I could never have something like this back in Australia. Anyhow, i put 250 rounds through it on Christmas day, and went to clean it that night. While cleaning i noticed 2 marks inside the top of the receiver. They seem to have worn quite a way through the nickel plating. Not knowing anything about guns, (i am however very mechanically inclined. restored plenty of muscle cars and built a chopper or 2) the wear marks just seem a little more heavy than they should be, can anyone tell me if this is normal for an 870? I fired all 2 3/4 shells except for one box that were 3 inch (man it was fun) Yesterday i put another 450 rounds through it and the action has already gotten really nice. In the firs 200 rounds i had a couple of stiff ejects. But after cleaning and oiling, yesterday i had not a single issue, even with the crap wally world ammo im using. Point is, the marks are a little more "worn" looking now than they were after the first 200 rounds. Anyway, is this anything i should worry about?? Will it just wear out enough to create clearance for whatever is rubbing and that will be that. Or is it something that will finally wear down enough to fail. I get the idea how the whole mechanism works i just cant really figure whats causing that? Thanks so much for your time. Proud to be American!!!! Sam.