Occasionally questions arise about the side sling swivel for the AR15/M16/M4. This will answer a few common questions.
It is normal for the sling mount to move. it will wear and make marks on the barrel.
Side sling swivels come from the factory mounted so the loop faces the rear of the rifle. This is fine if your using CAR or M4 plastic hand guards. However if you are using a Knights M4 RAS this loop will interfer with installing and removing rail panel covers. The Army authorizes mounting the sling loop forwards to negate that issue.
If you are mounting a M203 underbarrel grenade launcher on a M4, the side sling swivel will need to be mounted so the loop is on the ejector port side of the rifle(same side as used for left handed shooters).