Mossberg 930 JM

[Nelly2014]

TF for the internet.
I was cleaning the beast last night and hit a snag. The gas check would not slide over the mag tube. Then a totally random split ring appeared and I could not see where it had to go. This is not in the manual or appear in any exploded diagrams I looked at. However, I eventually found something by putting 'JM pro mystery ring' in google. Someone else had had the same problem and they put detailed pics and info to show where it goes.
I've also seemed to have lost one of the grub screws off the top of the receiver, bugger.