I have that same problem with my Bushmaster.
I haven't tried this yet, the foil seems a little mickey mouse to me, but I pulled it off here a LONG time ago....don't know who posted it, but here it is
I have a cheap solution for you. I had the same problem with my Colt and
fixed it using the following method--it works. Please excuse me if my use of
terminology is a bit confusing:
If you remove your handguards, you will notice that under the delta ring,
there is a sprocket-like thing with scalloped-out indentations. If you look
on the underside of each handguard, you will notice that there is a small
groove at the near end of the handguard with a raised bump or bumps in it.
That bump is supposed to engage the scallops in the sprocket underneath the
handguard and keep it from moving. Problem is, the bump is too small to stop
the whole thing from wigglin'
What you want to do is take some alum. foil and fold it up so it fills the
groove in the handguard. It will stay in the groove on its own accord once
the handguards are put in place and the delta ring slipped over it. A little
trial and error is required to get the right amount of foil in the
groove--too much will prevent the delta ring from slipping over the
handguard--too little will not stop the thing from moving.
If I remember correctly, the foil kept falling out of the groove when I put
the handguards on. I stopped this by placing a piece of masking tape over
the goove with the foil in it and trimming the excess.
My handguards are now nice and firm. Give it a shot and let me know if it
worked for you.