To the whole O ring thing...I tried putting an O ring around the lug and it would not close. So I took the O ring and just dropped it into the bottom of the hole the lug goes in and voila - no movement. Have not fired it with the O ring "installed" yet but hopefully next weekend.
FYI...Mine had no wobble when I first got it but after some rounds through it, it wobbled slightly.
Edit...I had some issues with the O ring dumped in the bottom of the lug hole. I used a thinner O ring around the lug and things look good no