The first question is what type of setup are you running?
The first thing that I would do is run a chamber brush in the chamber brush (on a cleaning rod section) with a power drill for roughly 10-25 seconds to clean any excessive coating in the chamber.
If it still has a problem I would check to see if it is a .223 chamber running 5.56 ammo, if so then that would expain the problem.
If you have a 5.56 chamber then I would try an A-2 (or A-1) buttstock, if it is still occuring then I would check the gas rings to see if they are aligned.
If it is still malfunctioning then it very well may be a problem with the carrier assy.
If you still have problems let me know via e-mail or the phone.