The handguards on one of my mid-length RRAs are pretty loose.  Is there a field expediant way to get them to stop shifting around and rattling?

Please don't suggest that I get a KAC or SIR or other freefloat, I'm simply looking to firm up the system I've got.

I had a little movement in the guards on my 16" Bushmaster.  The movement didn't bother me until I started using a vertical grip, then it was more pronounced.  I wrapped a little 550 paracord around the center of the guards.  Problem solved.

I'd be interested in reading what others have done to remedy this problem.

Had the same problem with my BM M4-type handguards.  I also didn't notice it until I installed a vertical foregrip.  Basically the front of the handguard was moving vertically within the handguard cap.
I fabricated a little X-shaped spacer out of plastic from a 22lr cartrige holder (the ones that come in 50rd boxes).  Put the spacer in the notch in the front of one of the handguards, and reinstalled the handguards.  No more rattle.
I don't know how much heat the plastic will take since I don't get my barrel very hot.

Try wrapping some rubber friction tape like an electrician would use it has no adhesive and is readily available from hardware stores , pull the delta ring down and wrap some very tightly in the space after your delta ring is pulled down and let it go it will force the handguard forward and tighten it up , or put it in the halves like a gasket !

I 'tightened' up my handguards that were loose by putting some JB Weld at each of the two contact points on the font of each hanguard.  Then I let the JB Weld cure overnight and used a file to remove a little material at a time, until each handguard fit the handguard retaining cap just behind the front sight.

It works pretty well, but if you are in the habit of removing and replacing your handguards frequently, you'll need to repeat the process.

HTH,

Josh