[b]I have had some handguards that fit real loose on one barrel and then tight on another. I wonder if the barrel nut makes the difference. At any rate, I use new Colt carbine handguards on all my uppers as well as new barrel nuts. Some are still loose. The way I tighten them up is to take some silicone putty and put it around the teeth and indentations at the base of the handguard where it contacts the teeth of the barrel nut. Press into place and let it setup for 24 hours, and you will have handguards with no play in them.
Charles Tatum
Alamo Professional Arms[/b]
Some one else on this board also recommended this type of fix by using the PERMATEX black HI-temp RTV silicon. I have done this to my shorty, just waiting on a good day to go to the range and test it. So far it looks like it will work and the black RTV blends in with the rest of the rifle. Overflow trimmed right off using a razor blade.