frag316

Hey, all, Just picked up a Super 90 M1 (S/N 3012XX). Have no idea when it was made or anything. No box, just the shotgun and a Full choke tube. (Price was right, $499, paid $267 cash after trading my 11/12-year old Remington 1100.) It was filthy, so I took it down (downloaded the manual from the website) and cleaned it thoroughly. Put it back together, seems to work OK (haven't shot it yet . . . ). Two questions: 1) I've got this blued metal disk about 5/8" in diameter with a 1/8" hole in the center. Don't remember where it came from, currently residing beneath my magazine tube cap. Can anyone tell me where it's supposed to go? 2) I'm looking at putting a mag extension tube on this bad boy (I'm looking to shoot IPSC with it), but when I unscrew the cap and look at the end of the magazine tube, the piece of metal there doesn't look like it's supposed to come out. Can anyone tell me whether/how I can remove it to put a mag extension on? Thanks in advance! Frag