So you say the barrel nut is tight. The delta ring is just loose as in not tight and springy? If that's the case buying a new delta ring spring should fix it.
This is more or less what your front end should look like http://www.militaryphotos.net/forums...=1#post1433095
, the front of the handguard against the front ring at the triangle sight and the delta ring fit against it by the spring tension from the delta ring spring.
Note that you can't use a whole real steel delta ring assy due to the different thread pitch on airsoft vs real steel (except for G&P uppers which use a real steel thread pitch). However you should be able to use the delta ring and spring part if you manage to get your hands on one. They should be fairly cheap, for the whole assy you're looking at like $20-25 at a gun store and just ditch the barrel nut and use the ring and spring.