I noticed on my Bren 2MS that the stock adapter piece had a lot of slop. After a quick search of teh internetz, I discovered I'm not alone. I read about a couple of fixes people have used ranging from smashing down a washer, using electrical tape, and using duct tape, all in an effort to shim the piece.
What I did was remove the sling adapter, which is held in place by a single countersunk torx screw; I then cut a "ranger band" into a small rectangular piece, used a leather punch to make a hole for the screw, and then sandwiched that between the sling adapter and the upper to which it attaches. The thickness of the ranger band was perfect, and has enough give to allow for some compression. This allows you to snug the sling adapter so that it is perfectly flush with the upper receiver, and creates just enough tension when snapping the stock adapter in place that it no longer wobbles.
Now to head to the range and see how it holds up.
