Check the markings on your barrel, check here for chamber specs ...
http://groups.msn.com/TheMarylandAR15ShootersSite/ar15brands.msnw
and contact the manufacturer to be sure.
Also, excessive residue build-up, especially in the neck area of the chamber or in the barrel extension area where the bolt lugs turn and lock, can have the same effect as a headspace problem, especially on a new gun.
Tolerances here are in thousandths of inches.