I just received a set of M4 handguards.  They are loose in the front band.  Is there a solution to this problem?

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There are several things I do to "silence" AR type rifles (and not just with M4 handguards).

(1)Put a thin bead of black silicone, the automotive gasket type, which does not have acetic acid (vinegar smell) and thus will not corrode, in the handguard where the "teeth" of the barrel nut engage in the back, and where the front portion contacts the handguard cap.  Let any excess ooze and harden, don't wipe it as it will smear.  Then just cut with a sharp knife and peel away excess.

(2) A nylon Ty-wrap (cable tie) around the base of the front swivel will still allow movement, but silence the rattle.

(3) If upper to lower fit is wobbly, use an Accuwedge.

This will make for a very quiet rifle, no creeks, groans, or rattles.

Also, the handguard may still be easily removed for cleaning.

JB Weld worked for me. Read the link Red-Leg posted.